Personal Computer

PERSONAL COMPUTER •

Computer (PC)

Typographies • • •

Types of computers Laptop computer PDA

Computer heart • • •

Processor Mother board Casing

Memory • • • •

Memory Random access memory (RAM) Read-only memory (ROM) Flash memory

Memory cards • • • • • •

Compact Flash (CF) Memory stick (MS) Multimedia Card (MMC) Secure Digital (SD) Smartmedia (SM) xD Picture card

• • • • •

Bus ISA, MCA, VLB PCI AGP PCI Express

• • • • • • •

Serial/parallel port USB FireWire IDE / ATA Serial ATA SCSI PC Card (PCMCIA)

Bus

I/O

Periphery Equipment • •

Periphery Equipment Hardware Interrupts (IRQ/DMA)

Display Periphery Equipment • • •

Screen/Monitor Cathode Ray Tube LCD/Plasma

Mass Storage Periphery Equipment • • • •

Hard Drive disc CD-ROM player DVD-ROM player USB key

Others Periphery Equipment • • • • •

Keyboard Mouse Printer Scanner Modem

Expansion cards • • • BIOS BIOS

Graphics card Sound card Network adapter

Introduction to the Concept of the Computer Understanding computer vocabulary is the main difficulty that potential personal computer buyers face. Unlike buying a TV, a task for which the decision-making criteria are limited, choosing a computer requires choosing each of its components and knowing their characteristics. The purpose of this document is not to make sense of all the computer abbreviations (because each manufacturer has their own technologies) but rather to profile the main components of a computer, explain how they work and outline their main characteristics. Presentation of the Computer A computer is a set of electronic circuits that allow for data to be manipulated in binary form, i.e. in bits. Types of Computers Any machine capable of manipulating binary information can be considered a computer. However, the term "computer" is sometimes confused with the term personal computer (PC), which is the type of computer that is most commonly found on the market. And yet there are many other types of computers (the following is not an exhaustive list): •

Amiga

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Atari

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Apple Macintosh

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Alpha stations

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SUN stations

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Silicon Graphics stations

The rest of this document, as generic as it might be, applies particularly to PC type computers. They are also called IBM-compatible computers because IBM is the company that created the first of these computers models and was for a long time (until 1987) the leader in this area, so much so that they controlled the standards, which were copied by other manufacturers. Make-up of a Computer A computer is a collection of modular electronic components, i.e. components that can be replaced by other components that may have different characteristics that are capable of running computer programs. Thus, the term "hardware" refers to all the material elements of a computer and "software" refers to the program parts. The material components of the computer are structured around a main board that is made up of a few integrated circuits and many electronic components such as capacitors, resistors, etc. All these components are fused to the board and are linked by circuit board connections and by a large number of connectors. This board is called the motherboard.

The motherboard is housed in a casing (or frame) that comprises slots for memory peripherals on the front, buttons that allow you to switch the computer on and off, as well as a certain number of indicator lights that allow you to verify the computer's operating state and the activity of the hard drives. On the back, the casing has openings facing the expansion boards and the I/O interfaces, which are connected to the motherboard. Finally, the casing houses an electrical power supply (commonly called the power), which is in charge of providing a stable and continuous electrical current to all of the elements that make up the computer. The power supply converts alternating current from the power grid (220 or 110 volts) into a direct voltage of 5 volts for the computer components and 12 volts for some internal peripherals (drives, CD-ROM drives, etc.). How powerful the electrical supply is determines how many peripherals the computer is capable of supplying. The power supply is generally between 200 and 450 Watts. The "central processing unit" includes the casing and all the elements it contains. The external elements of the central processing unit are called peripherals. The central processing unit must be connected to a whole set of external peripherals. A computer generally comprises at least the central processing unit, a screen (monitor), a keyboard and a mouse, but it is possible to connect a wide range of peripherals on the I/O interfaces (serial ports, parallel ports, USB ports, FireWire ports, etc.): •

a printer

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a scanner

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an external sound card

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an external hard drive

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an external storage peripheral

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a digital camera or video camera

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a PDA

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etc.

Types of computers There are several families of computers, depending on their format: •

Mainframes, computers which a great deal of computing power, enormous input-output capabilities and high level of reliability. Mainframes are used by large companies to carry out heavy computing operations are large volumes of data processing. Mainframes are normally used in centralised architectures, in which they are the heart.

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Personal computers, including, o

Desktop computers, made up of a case which houses a motherboard and allows users to connect multiple peripheral devices such as the screen.

o

Laptop computers, made of a case with a fold-out screen, a keyboard, and many onboard devices.

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Tablet PCs, made of a case which integrates a touch-screen and a certain number of onboard devices.

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Media centres, which represent a hardware platform, intended to be used in living rooms for running hifi elements (such as a hifi sound system, television set, DVD player, etc.)

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Personal digital assistants (called PDAs, or handhelds), sometimes known as organisers or electronic datebooks, are pocket computers with features for personal organisation.

Laptop Computer Relegated several years ago only to business use, laptop computers now have processing and storage capabilities close to that of desktop computers, and can easily be used for high-tech multimedia purposes (DVD drive, video games, 3Dimage processing, etc.). If the price of a laptop computer is still higher than that of a desktop computer because of its mobility, its use is also more varied because of the fact that can be taken virtually anywhere. However, given its reduced size, most of a laptop computer's pieces are integrated and therefore cannot be changed. This is why users must choose their laptop's characteristics once they are well-informed and have their planned use in mind. On the other hand, the fact that the manufacturer integrates the components allows for reduced risk of hardware incompatibilities (hardware conflicts). What is a Laptop Computer? A laptop computer (also called notebook computer) is a computer that integrates all the elements that needs to run properly, including a battery power supply, a screen and a keyboard, in a small casing (on average 360 cm x 40 cm x 270 cm).

Why a Laptop? The main advantage of a laptop computer versus a desktop computer is its mobility as well as its reduced size. On the other hand, the price is generally higher for slightly less impressive performance and the laptop's hardware configuration is much

less adaptable, even though it is possible to connect additional external peripherals thanks to its numerous I/O ports. Therefore, the motivation for buying a laptop computer must above all be a need for mobility or a need to save space. Moreover, with the emergence of wireless networks, and WiFi in particular, it is becoming very easy to connect to the Internet in public Hot-Spots or simply in any room of your home as long as it is equipped with a WiFi terminal. For advanced multimedia uses (e.g. digital video manipulation, connecting a digital camera or an mp3 player, etc.), the choice should fall on both the computer's performance (both graphic as well as computing power) and on the types and number of I/O ports that are available. Processor and RAM The processor represents the computer's brain in that it processes the instructions. Its execution speed depends on its frequency (in MHz), but two processors from different brands that have very different frequencies can perform equally. Even though a processor's frequency is still an essential criterion for choosing a laptop computer, today it is preferable to favour the quality of all the components (graphics card, memory, etc.) over only the processor's frequency. What is more, the quantity of random access memory (RAM) can have a considerable effect on performance, notably when it comes to multimedia use. In addition to the quantity of memory, it is also important to pay attention to its working frequency, which corresponds to the frequency that most of the peripherals will run on. Screen Laptop computers have flat screens. Most of the time they are active matrix screens (generally with the TFT, Thin Film transistor technology), i.e. each pixel is individually controlled, allowing for improved display fluidity over passive matrix screens, on which pixels are controlled by line and by column. The latest generations of laptops have favoured active matrix screens over passive matrix screens. The screen is distinguished first of all by its size, which is expressed in inches (an inch equals 2.54 cm) and corresponds to the screen's diagonal length. Unlike screens with cathode ray tubes (CRT screens), the diagonal length of a flat screen corresponds to the effective display area. Moreover, considering the liquid crystal based technologies used in flat screens, the screen quality of a flat screen can be defined by the response time, which is the length of time necessary to turn a pixel from white to black and then back to white. The display format is generally 4:3 (i.e. 4 units wide to 3 units high), but there are more exotic laptop display formats that are close to 16:9, such as 15:10, which is adapted to viewing video sequences (e.g. watching DVDs). In general, this type of screen has does not have a whole number diagonal length (e.g. 15.4 inches). Hard Drive The hard drive is the area where all the computer's data is stored unlike the RAM, which is a volatile memory that only acts as an information transit area while the computer is running. The most important characteristic of the hard drive is its capacity (expressed in gigabytes), because it determines the amount of data (and, in particular, programs) that a user can store on it. However, it is a good idea to pay

particular attention to its performances (in relation notably to its spindle speed), which can hamper the system's overall capacities if they are too weak. Using external hard drives (FireWire or USB 2.0) can nevertheless enhance a laptop computer by wiping out the intrinsic limitations of its standard hard drives and extending its storage capacity ad infinitum. Graphics Card A laptop computer's graphics card is integrated, i.e. it is a specialised graphics chip (graphic chipset) that is soldered to the motherboard. It is impossible to change it once the laptop has been purchased. Therefore, if the laptop computer will be used for graphics applications (video visualisation or manipulation, video games, 3D applications, etc.), it is best to choose a top-of-the-line graphics chipset. CD/DVD Drive or Burner More and more laptop computers are making a CD-ROM or a DVD-ROM drive or even a burner into standard features on high-level configurations. When the drive combines several of these functions, it is called a "combo". There are different types of CD (with a capacity of about 700 Mb) and DVD (with a capacity of about 4.7 Gb) burners. •

The term "CD-R" refers to recordable compact disks

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The term "CD-RW" refers to rewritable compact disks

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The term "DVD-R" refers to recordable DVDs

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The term "DVD-RAM" refers to rewritable DVDs Thus, there are two incompatible standards promoted by different manufacturer consortiums: o

DVD+RW, by Philips, that have performances in terms of recording time that are generally slightly better than the DVD-RW format

o

DVD-RW, which cost slightly less than DVD+RWs

It should be noted that some burners support both of these standards and thus are called "multi-format" burners. Input/Output Interfaces Input/output interfaces allow you to extend a laptop computer's functionalities by connecting external peripherals. Laptops generally have PC Card connectors (PCMCIA) that allow you to insert additional peripherals. USB ports are available on all recent laptop computers but it is a good idea to verify if they are USB 1.0 ports, which offer a peak throughput of 12 Mbit/s, or USB 2.0 ports, which can have a peak throughput of up to 480 Mbit/s! Having IEEE 1394 ports (with the commercial name of FireWire on Apple machines and i.LINK on IBM compatible machines) is a good idea for those users acquiring video from a DV digital video camera. FireWire ports allow throughputs on the order of 800 Mbit/s! Some laptops come standard with multi-card readers that can read flash memories in the following different formats: Secure digital (SD Card), Multimedia Card (MMC),

Memory stick (MS), SmartMedia (SM), Compact Flash (CF) or xD picture card. This type of reader can be extremely practical for those people who have MP3 players, digital cameras or personal desktop assistants (PDAs) because it facilitates the direct copying of files (e.g. music or digital photos) at a high bandwidth. Audio and Video Input/Output Every laptop computer has a screen and internal speakers but in some circumstances it is useful or even necessary to connect it to higher performance stereo or video systems (e.g. for a presentation or for a DVD projection). Laptop computers come standard with a VGA connector, which allows you to connect them to an external monitor or a video projector. Sometimes laptops come equipped with a video output (called a TV output), i.e. a S-Video connector that allows you to connect the computer directly to a television. With regard to audio I/O, all laptop computers come with standard headphone and microphone jacks as well as stereo speakers of varying quality. Having a S/PDIF output (digital audio output) can allow users to connect their laptop to a sound system that supports Dolby Digital 5.1 (e.g. for Home Cinema use). Pointing Device / Keyboard Laptop computers come standard with an integrated keyboard and pointing device. The pointing device is generally a touchpad, i.e. a flat touch-sensitive surface that allows you to move the cursor like a mouse. Some laptops come equipped with a trackpoint, i.e. a little touch-sensitive eraser-like tip (generally red) located in the middle of the keyboard that allows users to move the cursor with their fingers. The keyboard and pointing device should be chosen according to their ergonomics. They should be tried out in order to determine if they are comfortable to use. It should be noted that nothing prevents users from connecting a traditional mouse to a laptop computer for more comfort. Mobility and Network Connectivity In the communications world that we live in today, it is impossible to imagine a laptop computer without network functionalities. The terms nomadism and mobility are used to refer to individuals' capacity to have access to their information over the Internet, no matter where they are. Most laptop computers come standard equipped with a 56K V90 modem that allows them to connect to the Internet over the telephone network (STN, switched telephone network). The "10/100 Mbit Fast Ethernet" connector can be used to connect a laptop to a local area network (LAN) or to connect it to network equipment such as an ADSL modem, a router, a switch or even directly to another computer with a crossover network cable. With the emergence of wireless networks and the increased number of public and private wireless network access points (called hot spots), the concept of nomadism is taking on a whole new meaning. Thus, some laptop computers now come standard with built-in or card WiFi adapters. WiFi technology allows computers equipped with specialised adapters (WiFi cards) to connect with each other over a range of several

dozen or even hundreds of meters and possibly even to connect to the Internet thanks to a wireless router (WiFi terminal). There are several WiFi standards that use different transmission channels: •

WiFi 802.11a for a throughput of 54 Mb/s (30 Mb/s of real throughput)

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WiFi 802.11b for a throughput of 11 Mb/s (6 Mb/s of real throughput) with a range of up to 300 meters in an open environment

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WiFi 802.11g for a throughput of 54 Mb/s (30 Mb/s of real throughput) on a frequency band of 2.4 GHz.

Some laptops are equipped with Bluetooth technology, which is another wireless network technology. However, it is used primarily for wireless personal area network (WPAN), i.e. it is intended for small wireless devices such as mobile phones, PDAs, etc. IrDa (infrared) technology allows users to connect small devices wirelessly to each other but, unlike BlueTooth technology, has distance limitations (several dozen centimetres facing each other) and reduced throughput. Technical Characteristics When you buy a laptop computers, in addition to choosing specific hardware elements you should carefully weigh the following characteristics: •

weight: a laptop computer is made to be transported, so it is important to choose the lightest one possible. Nevertheless, watch out for laptops that are light and have many external peripherals (CD-ROM/DVD-ROM drive, mouse, power supply, hubs, etc.)

•

autonomy: Computer autonomy depends on how much energy a computer's components use as well as the battery's characteristics o

NiCad (Nickel / Cadmium): a rechargeable battery that is now obsolete because it suffered from the memory effect, i.e. a progressive decrease in the maximum charge when it is recharged when it is not completely "dead"

o

NiMH (Nickel / Hybrid Metal): a rechargeable battery that works better than nickel-cadmium batteries

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Li-Ion (Lithium / Ion): a rechargeable battery used in most laptop computers. Li-Ion batteries perform well and are reasonably priced. Moreover, Li-Ion batteries do not suffer from the memory effect, which means that it is not necessary to run the battery dry before recharging it.

o

Li-Polymer (Lithium / Polymer): a rechargeable battery that is equivalent to Li-Ion batteries in terms of performance but is much lighter because the battery electrolytes and microporous separator in

Li-Ion batteries are replaced by a solid polymer that is much lighter. On the other hand, Li-Polymer batteries take longer to charge and their longevity is shorter

Generally, computer autonomy is expressed in the amount of time that a computer can remain in sleep mode and in use. •

Operating Temperature: Running certain parts of a laptop computer (particularly the processor) causes the temperature of the computer to increase and sometimes become bothersome (especially when the keyboard becomes too hot).

Overheating can become a real danger that can worsen when the laptop is running with the screen down because this can prevent proper thermal dissipation.

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noise: In order to dissipate the heat caused by the running of different parts of the laptop (especially the processor), laptop computers are sometimes equipped with heat evacuation devices, such as fans, that can create loud, bothersome noises. This is also true for that motors that run the hard drives and CD/DVD drives/burners. Therefore, it is a good idea for buyers to enquire about the level of noise the computer makes when it runs.

Docking Station Some laptops come with a docking station. This is the device that the laptop computer fits into in order to easily connect it with a keyboard, mouse, screen, etc. Warranty Buying a laptop computer is a big investment. Therefore it is necessary to protect yourself against the risks associated with computer failure by signing up for a warranty. The warranty is even more important for laptop computers because it is not possible to change parts (graphics card, sound card, etc.) like you can on desktop computers. Most offers automatically include at least one year but it might be a good idea to take a several year warranty extension in order to cover the maximum number of risks.

Make sure you get information about the type of damages that are covered by the warranty. Batteries in particular are rarely covered.

Software Package Laptop computers are almost systematically equipped with an operating system when you purchase them but some offers also include a whole package of useful

software such as office tools, an encyclopaedia or even antivirus software. It is a good idea to keep this in mind when you are buying a laptop. Protective Cover If you are going to travel with your computer, it is necessary to have a computer bag in order to protect it when transporting it with all its accessories. In addition, it is highly recommended that you invest in a security cable (Kensington ComboSaver), which allows you to attach the laptop to a fixed piece of furniture thanks to the standard notch that is found on almost all laptops on the market. Processor NextMother board

Introduction The processor (CPU, for Central Processing Unit) is the computer's brain. It allows the processing of numeric data, meaning information entered in binary form, and the execution of instructions stored in memory. The first microprocessor (Intel 4004) was invented in 1971. It was a 4-bit calculation device with a speed of 108 kHz. Since then, microprocessor power has grown exponentially. So what exactly are these little pieces of silicone that run our computers?

Operation The processor (called CPU, for Central Processing Unit) is an electronic circuit that operates at the speed of an internal clock thanks to a quartz crystal that, when subjected to an electrical currant, send pulses, called "peaks". The clock speed (also called cycle), corresponds to the number of pulses per second, written in Hertz (Hz). Thus, a 200 MHz computer has a clock that sends 200,000,000 pulses per second. Clock frequency is generally a multiple of the system frequency (FSB, FrontSide Bus), meaning a multiple of the motherboard frequency. With each clock peak, the processor performs an action that corresponds to an instruction or a part thereof. A measure called CPI (Cycles Per Instruction) gives a representation of the average number of clock cycles required for a microprocessor to execute an instruction. A microprocessor’s power can thus be characterized by the number of instructions per second that it is capable of processing. MIPS (millions of instructions per second) is the unit used and corresponds to the processor frequency divided by the CPI. Instructions

An instruction is an elementary operation that the processor can accomplish. Instructions are stored in the main memory, waiting to be processed by the processor. An instruction has two fields: •

the operation code, which represents the action that the processor must execute;

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the operand code, which defines the parameters of the action. The operand code depends on the operation. It can be data or a memory address.

Operation Code

Operand Field

The number of bits in an instruction varies according to the type of data (between 1 and 4 8-bit bytes). Instructions can be grouped by category, of which the main ones are: •

Memory Access: accessing the memory or transferring data between registers.

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Arithmetic Operations: operations such as addition, subtraction, division or multiplication.

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Logic Operations: operations such as AND, OR, NOT, EXCLUSIVE NOT, etc.

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Control: sequence controls, conditional connections, etc.

Registers When the processor executes instructions, data is temporarily stored in small, local memory locations of 8, 16, 32 or 64 bits called registers. Depending on the type of processor, the overall number of registers can vary from about ten to many hundreds. The main registers are: •

the accumulator register (ACC), which stores the results of arithmetic and logical operations;

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the status register (PSW, Processor Status Word), which holds system status indicators (carry digits, overflow, etc.);

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the instruction register (RI), which contains the current instruction being processed;

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the ordinal counter (OC or PC for Program Counter), which contains the address of the next instruction to process;

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the buffer register, which temporarily stores data from the memory.

Cache Memory Cache memory (also called buffer memory) is local memory that reduces waiting times for information stored in the RAM (Random Access Memory). In effect, the computer's main memory is slower than that of the processor. There are, however, types of memory that are much faster, but which have a greatly increased cost. The solution is therefore to include this type of local memory close to the processor and to temporarily store the primary data to be processed in it. Recent model computers have many different levels of cache memory: •

Level one cache memory (called L1 Cache, for Level 1 Cache) is directly integrated into the processor. It is subdivided into two parts: o

the first part is the instruction cache, which contains instructions from the RAM that have been decoded as they came across the pipelines.

o

the second part is the data cache, which contains data from the RAM and data recently used during processor operations.

Level 1 caches can be accessed very rapidly. Access waiting time approaches that of internal processor registers. •

Level two cache memory (called L2 Cache, for Level 2 Cache) is located in the case along with the processor (in the chip). The level two cache is an intermediary between the processor, with its internal cache, and the RAM. It can be accessed more rapidly than the RAM, but less rapidly than the level one cache.

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Level three cache memory (called L3 Cache, for Level 3 Cache) is located on the motherboard.

All these levels of cache reduce the latency time of various memory types when processing or transferring information. While the processor works, the level one cache controller can interface with the level two controller to transfer information without impeding the processor. As well, the level two cache interfaces with the RAM (level three cache) to allow transfers without impeding normal processor operation. Control Signals Control signals are electronic signals that orchestrate the various processor units participating in the execution of an instruction. Control signals are sent using an element called a sequencer. For example, the Read / Write signal allows the memory to be told that the processor wants to read or write information. Functional Units

The processor is made up of a group of interrelated units (or control units). Microprocessor architecture varies considerably from one design to another, but the main elements of a microprocessor are as follows: •

A control unit that links the incoming data, decodes it, and sends it to the execution unit:The control unit is made up of the following elements: o

sequencer (or monitor and logic unit) that synchronizes instruction execution with the clock speed. It also sends control signals;

o

ordinal counter that contains the address of the instruction currently being executed;

o •

instruction register that contains the following instruction.

An execution unit (or processing unit) that accomplishes tasks assigned to it by the instruction unit. The execution unit is made of the following elements: o

The arithmetical and logic unit (written ALU). The ALU performs basic arithmetical calculations and logic functions (AND, OR, EXCLUSIVE OR, etc.);

o

The floating point unit (written FPU) that performs partial complex calculations which cannot be done by the arithmetical and logic unit.

•

o

The status register;

o

The accumulator register.

A bus management unit (or input-output unit) that manages the flow of incoming and outgoing information and that interfaces with system RAM;

The diagram below gives a simplified representation of the elements that make up the processor (the physical layout of the elements is different than their actual layout):

Transistor To process information, the microprocessor has a group of instructions, called the "instruction set", made possible by electronic circuits. More precisely, the instruction set is made with the help of semiconductors, little "circuit switches" that use the transistor effect, discovered in 1947 by John Barden, Walter H. Brattain and William Shockley who received a Nobel Prize in 1956 for it. A transistor (the contraction of transfer resistor) is an electronic semi-conductor component that has three electrodes and is capable of modifying current passing through it using one of its electrodes (called control electrode). These are referred to as "active components", in contrast to "passive components", such as resistance or capacitors which only have two electrodes (referred to as being "bipolar"). A MOS (metal, oxide, silicone) transistor is the most common type of transistor used to design integrated circuits. MOS transistors have two negatively charged areas, respectively called source (which has an almost zero charge) and drain (which has a 5V charge), separated by a positively charged region, called a substrate). The substrate has a control electrode overlaid, called a gate, that allows a charge to be applied to the substrate.

When there is no charge on the control electrode, the positively charged substrate acts as a barrier and prevents electron movement from the source to the drain. However, when a charge is applied to the gate, the positive charges of the substrate are repelled and a negatively charged communication channel is opened between the source and the drain.

The transistor therefore acts as a programmable switch, thanks to the control electrode. When a charge is applied to the control electrode, it acts as a closed interrupter and, when there is no charge, it acts as an open interrupter. Integrated Circuits Once combined, transistors can make logic circuits, that, when combined, form processors. The first integrated circuit dates back to 1958 and was built by Texas Instruments. MOS transistors are therefore made of slices of silicone (called wafers) obtained after multiple processes. These slices of silicone are cut into rectangular elements to form a "circuit". Circuits are then placed in cases with input-output connectors and the sum of these parts makes an "integrated circuit". The minuteness of the engraving, written in microns (micrometers, written µm) defines the number of transistors per surface unit. There can be millions of transistors on one single processor. Moore's Law, penned in 1965 by Gordon E. Moore, cofounder of Intel, predicted that processor performance (by extension of the number of transistors integrated in

the silicone) would double every twelve months. This law was revised in 1975, bringing the number of months to 18. Moore’s Law is still being proven today. Because the rectangular case contains input-output pins that resemble legs, the term "electronic flea" is used in French to refer to integrated circuits. Families Each type of processor has its own instruction set. Processors are grouped into the following families, according to their unique instruction sets: •

80x86: the "x" represents the family. Mention is therefore made to 386, 486, 586, 686, etc.

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ARM

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IA-64

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MIPS

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Motorola 6800

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PowerPC

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SPARC

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...

This explains why a program produced for a certain type of processor can only work directly on a system with another type of processor if there is instruction translation, called emulation. The term "emulator" is used to refer to the program performing this translation. Instruction Set An instruction set is the sum of basic operations that a processor can accomplish. A processor’s instruction set is a determining factor in its architecture, even though the same architecture can lead to different implementations by different manufacturers. The processor works efficiently thanks to a limited number of instructions, hardwired to the electronic circuits. Most operations can be performed using basic functions. Some architecture does, however, include advanced processor functions. CISC Architecture CISC (Complex Instruction Set Computer) architecture means hardwiring the processor with complex instructions that are difficult to create using basic instructions. CISC is especially popular in 80x86 type processors. This type of architecture has an elevated cost because of advanced functions printed on the silicone. Instructions are of variable length and may sometimes require more than one clock cycle. Because CISC-based processors can only process one instruction at a time, the processing time is a function of the size of the instruction.

RISC Architecture Processors with RISC (Reduced Instruction Set Computer) technology do not have hardwired, advanced functions. Programs must therefore be translated into simple instructions which complicates development and/or requires a more powerful processor. Such architecture has a reduced production cost compared to CISC processors. In addition, instructions, simple in nature, are executed in just one clock cycle, which speeds up program execution when compared to CISC processors. Finally, these processors can handle multiple instructions simultaneously by processing them in parallel. Technological Improvements Throughout time, microprocessor manufacturers (called founders) have developed a certain number of improvements that optimize processor performance. Parallel Processing Parallel processing consists of simultaneously executing instructions from the same program on different processors. This involves dividing a program into multiple processes handled in parallel in order to reduce execution time. This type of technology, however, requires synchronization and communication between the various processes, like the division of tasks in a business: work is divided into small discrete processes which are then handled by different departments. The operation of an enterprise may be greatly affected when communication between the services does not work correctly. Pipelining Pipelining is technology that improves instruction execution speed by putting the steps into parallel. To understand the pipeline’s mechanism, it is first necessary to understand the execution phases of an instruction. Execution phases of an instruction for a processor with a 5-step "classic" pipeline are as follows: •

FETCH: (retrieves the instruction from the cache;

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DECODE: decodes the instruction and looks for operands (register or immediate values);

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EXECUTE: performs the instruction (for example, if it is an ADD instruction, addition is performed, if it is a SUB instruction, subtraction is performed, etc.);

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MEMORY: accesses the memory, and writes data or retrieves data from it;

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WRITE BACK (retire): records the calculated value in a register.

Instructions are organized into lines in the memory and are loaded one after the other.

Thanks to the pipeline, instruction processing requires no more than the five preceding steps. Because the order of the steps is invariable (FETCH, DECODE, EXECUTE, MEMORY, WRITE BACK), it is possible to create specialized circuits in the processor for each one. The goal of the pipeline is to perform each step in parallel with the preceding and following steps, meaning reading an instruction (FETCH) while the previous step is being read (DECODE), while the step before that is being executed (EXECUTE), while the step before that is being written to the memory (MEMORY), and while the first step in the series is being recorded in a register (WRITE BACK).

In general, 1 to 2 clock cycles (rarely more) for each pipeline step or a maximum of 10 clock cycles per instruction should be planned for. For two instructions, a maximum of 12 clock cycles are necessary (10+2=12 instead of 10*2=20) because the preceding instruction was already in the pipeline. Both instructions are therefore being simultaneously processed, but with a delay of 1 or 2 clock cycles. For 3 instructions, 14 clock cycles are required, etc. The principle of a pipeline may be compared to a car assembly line. The car moves from one workstation to another by following the assembly line and is completely finished by the time it leaves the factory. To completely understand the principle, the assembly line must be looked at as a whole, and not vehicle by vehicle. Three hours are required to produce each vehicle, but one is produced every minute! It must be noted that there are many different types of pipelines, varying from 2 to 40 steps, but the principle remains the same. Superscaling Superscaling consists of placing multiple processing units in parallel in order to process multiple instructions per cycle. HyperThreading HyperThreading (written HT) technology consists of placing two logic processors with a physical processor. Thus, the system recognizes two physical processors and behaves like a multitasking system by sending two simultaneous threads, referred to as SMT (Simultaneous Multi Threading). This "deception" allows processor resources to be better employed by guaranteeing the bulk shipment of data to the processor. Motherboard NextCasing

Introduction to motherboards

The primary component of a computer is the motherboard (sometimes called the "mainboard"). The motherboard is the hub which is used to connect all of the computer's essential components.

As its name suggests, the motherboard acts as a "parent" board, which takes the form of a large printed circuit with connectors for expansion cards, memory modules, the processor, etc. Characteristics There are several ways in which a motherboard can be characterised, in particular the following: •

the form factor,

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the chipset,

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the type of processor socket used,

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the input-output connectors.

Motherboard form factor The term "form factor" is normally used to refer to the motherboard's geometry, dimensions, arrangement, and electrical requirements. In order to build

motherboards which can be used in different brands of cases, a few standards have been developed: •

AT baby/AT full format is a format used in the earliest 386 and 486 PCs. This format was replaced by the ATX format, which shape allowed for better air circulation and made it easier to access the components;

•

ATX: The ATX format is an upgrade to Baby-AT. It was intended to improve ease of use. The connection device on an ATX motherboard is designed to make plugging in peripherals as easy as possible (for example, the IDE connectors are located beside the disks.) What's more, motherboard components are arranged in parallel, so as to improve heat removal. o

ATX standard: The ATX standard format is traditionally 305x244 mm. It includes an AGP connector and 6 PCI connectors.

o

micro-ATX: The microATX format is an upgrade to ATX, which has the same primary advantages in a smaller format (244x244 mm), with a lower cost. Micro-ATX includes an AGP connector and 3 PCI connectors.

o

Flex-ATX: FlexATX is an expansion of microATX which offers manufacturers greater flexibility when designing their computers. It includes an AGP connector and 2 PCI connectors.

o

mini-ATX: miniATX is a compact alternative to the format microATX (284x208 mm), and includes an AGP connector and 4 PCI connectors instead of 3 that come with microATX. It is mainly intended for miniPCs (barebone computers).

•

BTX: The BTX format (Balanced Technology eXtended), supported by Intel, is a format designed to improve upon the arrangement of components, so as to optimise air circulation, acoustics, and heat dissipation. The various connectors (memory slots, expansion slots) are aligned in parallel, in the direction in which air circulates. Additionally, the microprocessor is located in the front end of the case, by the air intake, where the air is freshest. The BTX power cord is the same as with ATX power supplies. The BTX standard defines three formats:

•

o

BTX standard, with standard dimensions of 325x267 mm;

o

micro-BTX, with small dimensions (264x267 mm);

o

pico-BTX, with much smaller dimensions (203x267 mm).

ITX: The ITX format (Information Technology eXtended), supported by Via, is an extremely compact format designed for miniature configurations such as mini-PC. There are two major ITX formats: o

mini-ITX, with small dimensions (170x170 mm) and a PCI slot;

o

nano-ITX, with extremely small dimensions (120x120 mm) and a miniPCI slot. For this reason, the choice of the motherboard (and its

form factor) depends on which case is chosen. The table below summarises the characteristics of the various form factors.

Form factor Dimensions ATX

Slots

305 mm x 244 mm AGP / 6 PCI

microATX 244 mm x 244 mm AGP / 3 PCI FlexATX

229 mm x 191 mm AGP / 2 PCI

Mini ATX

284 mm x 208 mm AGP / 4 PCI

Mini ITX

170 mm x 170 mm 1 PCI

Nano ITX

120 mm x 120 mm 1 MiniPCI

BTX

325 mm x 267 mm 7

microBTX

264 mm x 267 mm 4

picoBTX

203 mm x 267 mm 1

Integrated components The motherboard includes some on-board components, meaning that they are integrated into its printed circuitry: •

The chipset, a circuit which controls the majority of resources (including the bus interface with the processor, cache memory and random-access memory, expansion cards, etc.)

•

The CMOS clock and battery,

•

The BIOS,

•

The system bus and the expansion bus.

What's more, recent motherboards generally include a number of onboard multimedia and networking devices which can be disabled: •

integrated network card;

•

integrated graphics card;

•

integrated sound card;

•

upgraded hard drive controllers.

The chipset

The chipset is an electronic circuit whose job is to coordinate data transfers between the various components of the computer (including the processor and memory). As the chipset is integrated into the motherboard, it is important to choose a motherboard which includes a recent chipset, in order to maximise the computer's upgradeability. Some chipsets may include a graphics or audio chip, which means that it is not necessary to install a graphics card or sound card. However, it is sometimes advised to disable them (whenever possible) in the BIOS setup and to install high-quality expansion cards in the appropriate slots. The CMOS clock and battery The real time clock (or RTC for short) is a circuit which synchronises system signals. It is made from a crystal which, as it vibrates, gives off pulses (called timer ticks) in order to keep the system elements running on the same time. The timer frequency (expressed in MHz) the number of times the crystal vibrates each second, i.e. the number of timer ticks per second. The higher the frequency, the more information the system can process. When the computer is turned off, the power supply stops providing electricity to the motherboard. When the computer is turned on again, the system is still on the right time. An electronic circuit, called the CMOS (Complementary Metal-Oxyde Semiconductor, sometimes called the BIOS CMOS), saves some system information, such as the time, the system date, and a few essential system settings. The CMOS is kept powered by a battery (a button battery), or a battery located on the motherboard. Information on the hardware installed in the computer (such as the number of tracks or sectors on each hard drive) are stored in the CMOS. As the CMOS is a form of slow storage, certain systems sometimes recopy the CMOS's content into the RAM (fast storage); the term "memory shadow" is used to describe this process of copying the data into RAM. The "complementary metal-oxide semiconductor" is a transistor manufacturing technology, the latest in a long line which includes the TTL ("Transistor-transistorlogic"), the TTLS (TTL Schottky) (faster), or the NMOS (negative channel) and PMOS (positive channel). The CMOS allows many complementary channels to run on a single chip. Compared with TTL or TTLS, CMOS is much slower, but it consumes far less energy, which is why it is used in computer clocks, which run on batteries. The term CMOS is sometimes incorrectly used to refer to computer clocks. When the system time keeps getting reset, or the clock runs late, all that is usually necessary is to change the battery. The BIOS The BIOS (Basic Input/Output System) is the basic program used as an interface between the operating system and the motherboard. The BIOS is stored in ROM (read-only memory, which can not be rewritten), so it uses data contained within the CMOS to find out what the system's hardware configuration is. The BIOS can be configured using an interface (named the BIOS setup), which can be accessed when the computer is booting just be pressing a key (usually the DEL key. In reality, the BIOS setup is only used as an interface for configuration; the data is stored in the CMOS. For more information, check your motherboard's manual.) The processor socket The processor (also called the microprocessor) is the computer's brain. It runs programs using a set of instructions. The processor is characterised by its frequency,

the rate at which it executes instructions. This means that an 800 MHz processor can carry out 800 million operations per second. The motherboard has a slot (sometimes several, for multi-processor motherboards) into which the processor is inserted, called the processor socket or slot. •

Slot: A rectangular connector into which the processor is mounted vertically.

•

Socket: In addition to being the general term, it also refers more specifically to a square-shaped connector with many small connectors into which the processor is directly inserted.

Within these two large families, there are different versions used, depending on the type of processor. Whatever slot or socket is used, it is essential that the processor be inserted gently, so that none of its pins are bent (it has hundreds of them). To make inserting them easier, a concept called ZIF (Zero Insertion Force) has been created. ZIF sockets have a small lever, which, when lifted, allows the processor to be inserted without applying any pressure, and when lowered, it holds the processor in place. The processor generally includes some sort of foolproof device, in the form of a notched corner or coloured markings, which must be aligned with the corresponding markings on the socket.

Since the processor releases heat, it is necessary to dissipate it, to keep the circuits from melting. This is why it is generally mounted atop a heat sink (sometimes called a cooler or radiator), which is made of a metal which conducts heat well (copper or aluminium) in order to increase the microprocessor's heat transfer surface. The heat sink includes a base in contact with the processor and fins in order to increase the heat transfer surface. A fan generally accompanies the cooler in order to improve air circulation around it and to improve the heat transfer. The unit also includes a fan which vents hot air from the case and let fresh air come in from outside. RAM connectors RAM (Random Access Memory) is used to store data while the computer is running; however, its contents are wiped out as soon as the computer is switched off or

restarted, as opposed to mass storage devices such as hard drives, which keep information safe even while turned off. This is why RAM is called "volatile." Why, then, is RAM used at all, when hard drives cost less per byte stored? The answer is that RAM is extremely fast when compared to mass storage devices like hard drives. It has a response time on the order of a few dozen nanoseconds (about 70 for DRAM, 60 for EDO RAM, and 10 for SDRAM; as little as 6 ns for DDR SDRAM) as opposed to a few milliseconds for a hard drive. RAM comes in the form of modules which plug into motherboard connectors. Expansion slots Expansion slots are compartments into which expansion cards can be inserted. These are cards which give the computer new features or increased performance. There are several types of slots: •

ISA slots (Industry Standard Architecture): For inserting ISA slots. The slowest ones are 16-bit.

•

VLB slots (Vesa Local Bus): Bus formerly used for installing graphics cards.

•

PCI slot (Peripheral Component InterConnect): used for connecting PCI cards, which are much faster than ISA cards and run on 32 bits

•

AGP slot (Accelerated Graphic Port): A fast port for a graphics card.

•

PCI Express slot (Peripheral Component InterConnect Express): Faster bus architecture than AGP and PCI buses.

•

AMR slot (Audio Modem Riser): This type of slot is used for connecting minicards to PCs which are built for it.

the input-output connectors. The motherboard has a certain number of input/output sockets found on the rear panel.

Most motherboards have the following connectors: •

A serial port, for connecting old peripherals;

•

A parallel port, mainly for connecting old printers;

•

USB ports (1.1, low-speed, or 2.0, high-speed), for connecting more recent peripherals;

•

RJ45 connector (called LAN or ethernet port) used for connecting the computer to a network. It corresponds to a network card integrated into the motherboard;

•

VGA connector (called SUB-D15), for connecting a monitor. This connector interfaces with the built-in graphics card;

•

Audio plugs (Line-In, Line-Out and microphone), for connecting sound speakers or a hi-fi system, as well as a microphone. This connector interfaces with the built-in sound card;

PC Case

NextMemory

The casing The case (or chassis) of a computer is the metallic box which houses the various internal components. Cases also have other uses, such as blocking noise produced by the computer, and protection from electromagnetic radiation. There are norms for guaranteeing such protection in a manner compliant with existing regulation.

The main considerations when choosing a case are its form factor, its dimensions, how many drive slots it has, its power requirements, the connectors it has on the

side, and finally its design and colour. Although the cases that housed the first PCs all looked alike, today cases come in all shapes; some are even transparent, so that users can "soup up" their computers, such as by installing neon lights inside (this is called "case modding.") Power supply Most cases come with a power supply. The power supply provides electrical current to all of the computer's components. In the United States and Canada, power supplies deliver 110V current at 60 Hz, while in Europe the standard is 220V at a frequency of 50 Hz, which is why most computer power supplies have a switch so that you can choose the voltage.

It is essential to make sure that the switch is in the correct position for the right voltage, so that there is no risk that the CPU components will deteriorate. The power supply must have enough power to provide electricity to all of the computer's devices. Close attention should also be paid to the amount of sound that the power supply makes. Form factor Form factor refers to the format of the motherboard slot, the kinds of connectors used, and how they are laid out. It determines which type of motherboard can be inserted in the case. Size The case's size affects how many slots are available for disk drives, as well as how many slots there are for internal hard drives. Cases are generally grouped by size as follows: •

Big tower: This is a large case (60 to 70 cm high), with four to six 5"1/4 slots and two to three slots each 3"1/2 on the side, as well as two to three internal 3"1/2 slots.

•

Medium tower: This is a medium-sized case (40 to 50 cm high), with three to four 5"1/4 slots on the side and two internal 3"1/2 slots.

•

Mini-tower: This is a small case (35 to 40 cm in height), typically with three 5"1/4 slots and two 3"1/2 slots on the side, as well as two internal 3"1/2 slots

•

Barebone or mini-PC: This is the smallest kind of case (10 to 20 cm high). Most barebone PCs are pre-assembled computers built with a small form factor (SFF) motherboard. They generally have one or two 5"1/4 slots and one 3"1/2 slot on the side, as well as one internal 3"1/2 slot.

Ventilation A case houses all of the computer's internal electronic components. Sometimes, a computer's electronics can reach very high temperatures. For this reason, you must choose a case with good ventilation, meaning that it has as many fans as possible, as well as air vents. It is recommended to choose a case which includes at least an air intake in front, a removable air filter, and an air outlet in the rear. Connections For obvious reasons involving ease of use, more and more cases are including a panel of connectors on the side. In order to work, these connectors must be hooked up internally to the motherboard. Computer - Introduction to Memory NextRandom access memory (RAM)

The Role of Memory The term "memory" applies to any electronic component capable of temporarily storing data. There are two main categories of memories: •

internal memory that temporarily memorises data while programs are running. Internal memory uses microconductors, i.e. fast specialised electronic circuits. Internal memory corresponds to what we call random access memory (RAM).

•

auxiliary memory (also called physical memory or external memory) that stores information over the long term, including after the computer is turned off. Auxiliary memory corresponds to magnetic storage devices such as the hard drive, optical storage devices such as CD-ROMs and DVD-ROMs, as well as read-only memories.

Technical Characteristics The main characteristics of a memory are: •

Capacity, representing the global volume of information (in bits) that the memory can store

•

Access time, corresponding to the time interval between the read/write request and the availability of the data

•

Cycle time, representing the minimum time interval between two successive accesses

•

Throughput, which defines the volume of information exchanged per unit of time, expressed in bits per second

•

Non-volatility, which characterises the ability of a memory to store data when it is not being supplied with electricity

The ideal memory has a large capacity with restricted access time and cycle time, a high throughput and is non-volatile. However, fast memories are also the most expensive. This is why memories that use different technologies are used in a computer, interfaced with each other and organised hierarchically.

The fastest memories are located in small numbers close to the processor. Auxiliary memories, which are not as fast, are used to store information permanently. Types of Memories

Random Access Memory Random access memory, generally called RAM is the system's main memory, i.e. it is a space that allows you to temporarily store data when a program is running. Unlike data storage on an auxiliary memory such as a hard drive, RAM is volatile, meaning that it only stores data as long as it supplied with electricity. Thus, each time the computer is turned off, all the data in the memory are irremediably erased. Read-Only Memory Read-only memory, called ROM, is a type of memory that allows you to keep the information contained on it even when the memory is no longer receiving electricity. Basically, this type of memory only has read-only access. However, it is possible to save information in some types of ROM memory. Flash Memory

Flash memory is a compromise between RAM-type memories and ROM memories. Flash memory possesses the non-volatility of ROM memories while providing both read and write access However, the access times of flash memories are longer than the access times of RAM. Random access memory (RAM or PC memory) NextRead-only memory (ROM)

Types of random access memory There are generally two broad categories of random access memory: •

DRAM memories (Dynamic Random Access Module), which are inexpensive. They are used essentially for the computer's main memory

•

SRAM memories (Static Random Access Module), which are fast and costly. SRAM memories are used in particular for the processor's cache memory

Operation of the random access memory The random access memory comprises hundreds of thousands of small capacitors that store loads. When loaded, the logical state of the capacitor is equal to 1, otherwise it is 0, meaning that each capacitor represents one memory bit. Given that the capacitors become discharged they must be constantly recharged (the exact term is refresh) at regular intervals, known as the refresh cycle. DRAM memories for example require refresh cycles of around 15 nanoseconds (ns). Each capacitor is coupled with a transistor (MOS-type) enabling "recovery" or amendment of the status of the capacitor. These transistors are arranged in the form of a table (matrix) thus we access a memory box (also called memory point) via a line and a column.

Each memory point is thus characterised by an address which corresponds to a row number and a column number. This access is not instant and the access time period is known as latency time. Consequently, time required for access to data in the memory is equal to cycle time plus latency time. Thus, for a DRAM memory, access time is 60 nanoseconds (35ns cycle time and 25ns latency time). On a computer, the cycle time corresponds to the opposite of the clock frequency; for example, for a computer with frequency of 200 MHz, cycle time is 5 ns (1/200*106)). Consequently a computer with high frequency using memories with access time much longer than the processor cycle time must perform wait states to access the memory. For a computer with frequency of 200 MHz using DRAM memories (and access time of 60ns), there are 11 wait states for a transfer cycle. The computer's performance decreases as the number of wait states increases, therefore we recommend the use of faster memories. RAM module formats There are many type of random access memory. They exist in the form of memory modules that can be plugged into the mother board. Early memories existed in the form of chips called DIP (Dual Inline Package). Nowadays, memories generally exist in the form of modules, which are cards that can be plugged into connectors for this purpose. There are generally three types of RAM module: •

modules in SIMM format (Single Inline Memory Module): these are printed circuit boards with one side equipped with memory chips. There are two types of SIMM modules, according to the number of connectors: o

SIMM modules with 30 connectors (dimensions are 89x13mm) are 8bit memories with which first-generation PCs were equipped (286, 386).

• o

SIMM modules with 72 connectors (dimensions are 108x25mm) are memories able to store 32 bits of data simultaneously. These memories are found on PCs from the 386DX to the first Pentiums. On the latter, the processor works with a 64-bit data bus; this is why these computers must be equipped with two SIMM modules. 30-pin modules cannot be installed on 72-connector positions because a notch (at the centre of the connectors) would prevent it from being plugged in.

•

modules in DIMM format (Dual Inline Memory Module) are 64-bit memories, which explains why they do not need pairing. DIMM modules have memory chips on both sides of the printed circuit board and also have 84 connectors on each side, giving them a total of 168 pins. In addition to having larger dimensions than SIMM modules (130x25mm), these modules have a second notch to avoid confusion.

It may be interesting to note that the DIMM connectors have been enhanced to make insertion easier, thanks to levers located either side of the connector. Smaller modules also exist; they are known as SO DIMM (Small Outline DIMM), designed for portable computers. SO DIMM modules have only 144 pins for 64-bit memories and 77 pins for 32-bit memories. •

modules in RIMM format (Rambus Inline Memory Module, also called RDRAM or DRD-RAM) are 64-bit memories developed by Rambus. They have 184 pins. These modules have two locating notches to avoid risk of confusion with the previous modules.

Given their high transfer speed, RIMM modules have a thermal film which is supposed to improve heat transfer. As for DIMMs, smaller modules also exist; they are known as SO RIMM (Small Outline RIMM), designed for portable computers. SO RIMM modules have only 160 pins. DRAM PM The DRAM (Dynamic RAM) is the most common type of memory at the start of this millennium. This is a memory whose transistors are arranged in a matrix in rows and columns. A transistor, coupled with a capacitor, gives information on a bit. Since 1 octet contains 8 bits, a DRAM memory module of 256 Mo will thus contain 256 * 2^10 * 2^10 = 256 * 1024 * 1024 = 268,435,456 octets = 268,435,456 * 8 =

2,147,483,648 bits = 2,147,483,648 transistors. A module of 256 Mo thus has a capacity of 268,435,456 octets, or 268 Mo! These memories have access times of 60 ns. Furthermore, access to memory generally concerns data stored consecutively in the memory. Thus burst mode allows access to the three pieces of data following the first piece with no additional latency time. In this burst mode, time required to access the first piece of data is equal to cycle time plus latency time, and the time required to access the other three pieces of data is equal to just the cycle time; the four access times are thus written in the form X-Y-Y-Y, for example 5-3-3-3 indicates a memory for which 5 clock cycles are needed to access the first piece of data and 3 for the subsequent ones. DRAM FPM To speed up access to the DRAM, there is a technique, known as paging, which involves accessing data located in the same column by changing only the address of the row, thus avoiding repetition of the column number between reading of each row. This is known as DRAM FPM (Fast Page Mode). FPM achieves access times of around 70 to 80 nanoseconds for operating frequency between 25 and 33 Mhz. DRAM EDO DRAM EDO (Extended Data Out, sometimes also called hyper-page") was introduced in 1995. The technique used with this type of memory involves addressing the next column while reading the data in a column. This creates an overlap of access thus saving time on each cycle. EDO memory access time is thus around 50 to 60 nanoseconds for operating frequency between 33 and 66 Mhz. Thus the RAM EDO, when used in burst mode, achieves 5-2-2-2 cycles, representing a gain of 4 cycles on access to 4 pieces of data. Since the EDO memory did not work with frequencies higher than 66 Mhz, it was abandoned in favour of the SDRAM. SDRAM The SDRAM (Synchronous DRAM), introduced in 1997, allows synchronised reading of data with the mother-board bus, unlike the EDO and FPM memories (known as asynchronous) which have their own clock. The SDRAM thus eliminates waiting times due to synchronisation with the mother-board. This achieves a 5-1-1-1 burst mode cycle, with a gain of 3 cycles in comparison with the RAM EDO. The SDRAM is thus able to operate with frequency up to 150 Mhz, allowing it to achieve access times of around 10 ns. DR-SDRAM (Rambus DRAM) The DR-SDRAM (Direct Rambus DRAM) is a type of memory that lets you transfer data to a 16-bit bus at frequency of 800Mhz, giving it a bandwidth of 1.6 Go/s. As with the SDRAM, this type of memory is synchronised with the bus clock to enhance data exchange. However, the RAMBUS memory is a proprietary technology, meaning that any company wishing to produce RAM modules using this technology must pay royalties to both RAMBUS and Intel. DDR-SDRAM The DDR-SDRAM (Double Data Rate SDRAM) is a memory, based on the SDRAM technology, which doubles the transfer rate of the SDRAM using the same frequency.

Data are read or written into memory based on a clock. Standard DRAM memories use a method known as SDR (Single Data Rate) involving reading or writing a piece of data at each leading edge.

The DDR doubles the frequency of reading/writing, with a clock at the same frequency, by sending data to each leading edge and to each trailing edge.

DDR memories generally have a product name such as PCXXXX where "XXXX" represents the speed in Mo/s. DDR2-SDRAM DDR2 (or DDR-II) memory achieves speeds that are twice as high as those of the DDR with the same external frequency. QDR (Quadruple Data Rate or quad-pumped) designates the reading and writing method used. DDR2 memory in fact uses two separate channels for reading and writing, so that it is able to send or receive twice as much data as the DDR.

DDR2 also has more connectors than the classic DDR (240 for DDR2 compared with 184 for DDR). summary table

The table below gives the equivalence between the mother-board frequency (FSB), the memory (RAM) frequency and its speed:

Memory

Name

Frequency (RAM)

Frequency (FSB)

Speed

DDR200

PC1600

200 MHz

100 MHz

1.6 Go/s

DDR266

PC2100

266 MHz

133 MHz

2.1 Go/s

DDR333

PC2700

333 MHz

166 MHz

2.7 Go/s

DDR400

PC3200

400 MHz

200 MHz

3.2 Go/s

DDR433

PC3500

433 MHz

217 MHz

3.5 Go/s

DDR466

PC3700

466 MHz

233 MHz

3.7 Go/s

DDR500

PC4000

500 MHz

250 MHz

4 Go/s

DDR533

PC4200

533 MHz

266 MHz

4.2 Go/s

DDR538

PC4300

538 MHz

269 MHz

4.3 Go/s

DDR550

PC4400

550 MHz

275 MHz

4.4 Go/s

DDR2-400

PC2-3200

400 MHz

100 MHz

3.2 Go/s

DDR2-533

PC2-4300

533 MHz

133 MHz

4.3 Go/s

DDR2-667

PC2-5300

667 MHz

167 MHz

5.3 Go/s

DDR2-675

PC2-5400

675 MHz

172.5 MHz

5.4 Go/s

DDR2-800

PC2-6400

800 MHz

200 MHz

6.4 Go/s

Synchronisation (timings) It is not unusual to see scores such as 3-2-2-2 or 2-3-3-2 to describe the parameterisation of the random access memory. This succession of four figures describes the synchronisation of the memory (timing), i.e. the succession of clock cycles needed to access a piece of data stored in the RAM. These four figures generally correspond, in order, to the following values: •

CAS delay or CAS latency (CAS meaning Column Address Strobe): this is the number of clock cycles that elapse between the reading command being sent and the piece of data actually arriving. In other words, it is the time needed to access a column.

•

RAS Precharge Time (known as tRP, RAS meaning Row Address Strobe): this is the number of clock cycles between two RAS instructions, i.e. between two accesses to a row. operation.

•

RAS to CAS delay (sometimes called tRCD): this is the number of clock cycles corresponding to access time from a row to a column.

•

RAS active time (sometimes called tRAS): this is the number of clock cycles corresponding to the time needed to access a row.

The memory cards are equipped with a device called SPD (Serial Presence Detect), allowing the BIOS to find out the nominal setting values defined by the manufacturer. It is an EEPROM whose data will be loaded by the BIOS if the user chooses "auto" setting. Error correction Some memories have mechanisms for correcting errors to ensure the integrity of the data they contain. This type of memory is generally used on systems working on critical data, which is why this type of memory is found in servers. Parity bit Modules with parity bit ensure that the data contained in the memory are the ones required. To achieve this, one of the bits from each octet stored in the memory is used to store the sum of the data bits. The parity bit is 1 when the sum of the data bits is an odd number and 0 in the opposite case. Thus the modules with parity bit allow the integrity of data to be checked but do not provide for error correction. Moreover, for 9 Mo of memory, only 8 will be used to store data since the last mega octet is used to store the parity bits. ECC modules ECC (Error Correction Coding) memory modules are memories with several bits dedicated to error correction (they are known as control bits). These modules, used mainly in servers, allow detection and correction of errors. Dual Channel Some memory controllers offer a dual channel for the memory. The memory modules are used in pairs to achieve higher bandwidth and thus make the best use of the system's capacity. When using the Dual Channel, it is vital to use identical modules in a pair (same frequency and capacity and preferably the same brand). Read-only memory (ROM) NextFlash memory

Read-only memory (ROM) There is a type of memory that stores data without electrical current; it is the ROM (Read Only Memory) or is sometimes called non-volatile memory as it is not erased when the system is switched off. This type of memory lets you stored the data needed to start up the computer. Indeed, this information cannot be stored on the hard disk since the disk parameters (vital for its initialisation) are part of these data which are essential for booting. Different ROM-type memories contain these essential start-up data, i.e.:

•

The BIOS is a programme for controlling the system's main input-output interfaces, hence the name BIOS ROM which is sometimes given to the readonly memory chip of the mother board which hosts it.

•

The bootstrap loader: a programme for loading (random access) memory into the operating system and launching it. This generally seeks the operating system on the floppy drive then on the hard disk, which allows the operating system to be launched from a system floppy disk in the event of malfunction of the system installed on the hard disk.

•

The CMOS Setup is the screen displayed when the computer starts up and which is used to amend the system parameters (often wrongly referred to as BIOS).

•

The Power-On Self Test (POST), a programme that runs automatically when the system is booted, thus allowing the system to be tested (this is why the system "counts" the RAM at start-up).

Given that ROM are much slower than RAM memories (access time for a ROM is around 150 ns whereas for SDRAM it is around 10 ns), the instructions given in the ROM are sometimes copied to the RAM at start-up; this is known as shadowing, though is usually referred to as shadow memory). Types of ROM ROM memories have gradually evolved from fixed read-only memories to memories than can be programmed and then re-programmed. ROM The first ROMs were made using a procedure that directly writes the binary data in a silicon plate using a mask. This procedure is now obsolete. PROM PROM (Programmable Read Only Memory) memories were developed at the end of the 70s by a company called Texas Instruments. These memories are chips comprising thousands of fuses (or diodes) that can be "burnt" using a device called a " ROM programmer", applying high voltage (12V) to the memory boxes to be marked. The fuses thus burnt correspond to 0 and the others to 1. EPROM EPROM (Erasable Programmable Read Only Memory) memories are PROMs that can be deleted. These chips have a glass panel that lets ultra-violet rays through. When the chip is subjected to ultra-violet rays with a certain wavelength, the fuses are reconstituted, meaning that all the memory bits return to 1. This is why this type of PROM is called erasable. EEPROM EEPROM (Electrically Erasable Read Only Memory memories are also erasable PROMs, but unlike EPROMs, they can be erased by a simple electric current, meaning that they can be erased even when they are in position in the computer.

There is a variant of these memories known as flash memories (also Flash ROM or Flash EPROM). Unlike the classic EEPROMs that use 2 to 3 transistors for each bit to be memorised, the EPROM Flash uses only one transistor. Moreover, the EEPROM may be written and read word by word, while the Flash can be erased only in pages (the size of the pages decreases constantly). Lastly, the Flash memory is denser, meaning that chips containing several hundred mega octets can be produced. EEPROMs are thus used preferably to memorise configuration data and the Flash memory is used for programmable code (IT programmes). The action involving reprogramming of an EEPROM is known as flashing. Memory card (Flash memory) NextCompact Flash (CF)

Introduction to Flash memory Flash memory is a kind of semiconductor-based, non-volatile, rewritable computer memory; that is, it has many of the same characteristics as RAM, except that the data is not wiped out when the machine is turned off. Flash memory stores bits of data in memory cells, but the data remains saved even when electrical power is cut. Due to its higher speed, durability, and low energy consumption, flash memory is ideal for many applications, such as digital cameras, mobile phones, printers, PDAs, laptop computers, and device that can record and play back sound, such as mp3 players. What's more, this kind of memory has no moving parts, which makes it very shock-resistant. Types of memory cards There are many competing, incompatible memory card formats, almost one for every manufacturer. Among these formats of memory cards, the most common are •

Compact Flash

•

Secure Digital cards (called SD Card)

•

Memory Stick

•

SmartMedia

•

MMC (MultimediaCard)

•

xD picture card

Comparison Dimensions (mm)

Volume (mm3)

Weight # of Transfer Theoretical (g) connectors rate capacity

Theoretical size

Compact Flash 43 x 36 x 3,3 5 108 type I

3,3

50

20 Mo/s

137 Go

128 Go

Compact Flash 43 x 36 x 5 type II

7 740

4

50

20 Mo/s

137 Go

12 Go

SmartMedia

37 x 45 x 0,8 1 265

2

22

2 Mo/s

128 Mo

128 Mo

MMC

24 x 32 x 1,4 1 075

1,3

7

20 Mo/s

128 Go

8 Go

MMC Plus

24 x 32 x 1,4 1 075

1,3

7

52 Mo/s

128 Go

4 Go

RS-MMC MMC 24 x 16 x 1,4 538 Mobile

1,3

13

8 Mo/s

128 Go

2 Go

MMC Micro

14 x 12 x 1,1 185

<1

13

128 Go

2 Go

Memory Stick Standard, Pro

21,5 x 50 x 2,8

4

10

2 Mo/s

128 Mo

128 Mo

Memory Stick Duo, Pro Duo

20 x 31 x 1,6 992

2

10

20 Mo/s

32 Go

16 Go

Memory Stick Pro-HG

20 x 31 x 1,6 992

2

10

60 Mo/s

32 Go

32 Go

Memory Stick Micro M2

12,5 x 15 x 1,2

2

10

20 Mo/s

32 Go

8 Go

SD

24 x 32 x 2,1 1 613

2

9

20 Mo/s

32 Go

32 Go

mini SD

20 x 21,5 x 1,4

602

1

11

12 Mo/s

32 Go

4 Go

micro SD

15 x 11 x 1

165

0,3

8

10 Mo/s

32 Go

12 Go

xD

25 x 20 x 1,8 890

2,8

18

9 Mo/s

8 Go

2 Go

3 010

225

Memory card readers It should be noted that there are multi-format memory card readers, most of which can be plugged into a USB port. Compact Flash memory card NextMemory stick (MS)

Compact Flash Compact Flash memory (sometimes called CF) is a kind of memory card created in 1994 by the company SanDisk. Compact Flash is made up of a memory controller and a flash memory chip contained within a miniature casing (42.8mm wide and 36.4mm high), which is smaller than a matchbox and weighs only 11.4 grams. There are two types of Compact Flash cards, with different dimensions: •

Type I Compact Flash cards, which are 3.3mm thick;

•

Type II Compact Flash cards, which are 5mm thick.

CompactFlash cards comply with the PCMCIA/ATA standard, although the connector has 50 pins instead of 68, as PCMCIA do. For this reason, a CompactFlash card can be inserted into a passive Type II PCMCIA slot Memory Stick (MS Card) NextMultimedia Card (MMC)

Memory Stick The Memory Stick (written as MS or MS Card) is a type of memory card created jointly by Sony and SanDisk in January 2000. The architecture of Memory Stick cards is based on NAND flash memory circuits (EEPROM). Memory stick memories are very small (21.5 mm x 50.0 mm x 2.8 mm), which is equivalent to the size of a small box of matches, and weigh only 4 grams.

Data can be accessed by way of an edge connector with 10 pins, for a throughput of up to 14.4 Mb/s (up to a maximum of 19.6 Mb/s).

There are two types of Memory Sticks: the "normal" Memory Stick and the "Magic Gate", which protects documents that are copyright protected. Multimedia Cards (MMC) NextSecure Digital (SD)

MMC - Multimedia Cards Multimedia card memory (abbreviated as MMC) is a type of memory card created jointly by SanDisk and Siemens in November 1997. Its architecture is based on a combination of read-only memory (ROM) for read-only applications and flash memory for read/write purposes. Multimedia cards are very small (24.0 mm x 32.0 mm x 1.4 mm), which is equivalent to the size of a postage stamp, and weigh only 2.2 grams.

There are two types of MMC cards that have different voltages: •

MMC 3.3V, with a notch on the upper left-hand corner

•

MMC 5V, with a notch on the upper right-hand corner

Data can be accessed by way of an edge connector with 7 pins, for a throughput of up to 2 Mb/s (perhaps even 2.5 Mb/s). SD Card (Secure Digital) NextSmartmedia (SM)

Secure Digital Secure Digital memory (known as SD or SD Card) is a type of memory card created by Matsushita Electronic, SanDisk and Toshiba in January 2000. Secure Digital memory is a memory specifically developed to meet new safety requirements in the field of electronic audio and video devices. It therefore includes a copyright protection system that satisfies the SDMI (Secure Digital Music Initiative) standard. The architecture of the SD cards is based on NAND-type flash memory circuits (EEPROM). The Secure Digital memory has small dimensions (24.0mm x 32.0mm x 2.1mm), equivalent to those of a postage stamp, and weighs barely 2 grammes.

Data are accessed using a 9-pin lateral connector achieving a transfer speed of 2 Mb/s with the potential to go up to 10 MB/s. SD memory access time is around 25µs for first access and cycles of 50 ns for subsequent cycles. SmartMedia cards NextxD Picture card

SmartMedia SmartMedia memory is a type of memory card created by Toshiba and Samsung. Its architecture is based on NAND type flash memory circuits (EEPROM) SmartMedia memory is equivalent in size to a postal stamp (45.0mm x 37.0mm x 0.76mm) and weighs barely 2 grams. There are two types of SmartMedia card with different voltages: •

3.3V SmartMedia cards have a notch on the right

•

5V SmartMedia cards have a notch on the left

Access to the data is carried out via a chip with 22 pins. Whatever the capacity of the SmartMedia card, the dimensions and location of the chip are the same.

Access time for the memory is approximately 25µs for the first access and cycles of 50 ns for the following ones. Compatibility There are two adapters making it possible to insert a SmartMedia card in a PCMCIA location, so as to enable the transfer of data directly from a SmartMedia card to a laptop. xD picture card NextBus

xD Picture card xD Picture memory (for eXtreme Digital) is a type of memory card created by Fuji and Olympus in August 2002. The architecture of xD cards is based on NAND type flash memory circuits (EEPROM) xD picture card memory is smaller in size than a postal stamp (20.0mm x 25.0mm x 1.7mm) and weighs barely 2 grams.

Access to the data is carried out via a lateral connector with 18 pins, allowing a transfer rate of 1.3 Mb/s to be reached and potentially up to 3Mb/s for writing and around 5 Mb/s for reading. In time it is expected that xD picture cards will reach a capacity of 8Gb. What is a computer bus? NextISA, MCA, VLB

Introduction to the concept of a bus A bus, in computing, is a set of physical connections (cables, printed circuits, etc.) which can be shared by multiple hardware components in order to communicate with one another. The purpose of buses is to reduce the number of "pathways" needed for communication between the components, by carrying out all communications over a single data channel. This is why the metaphor of a "data highway" is sometimes used.

If only two hardware components communicate over the line, it is called a hardware port (such as a serial port or parallel port). Characteristics of a bus A bus is characterised by the amount of information that can be transmitted at once. This amount, expressed in bits, corresponds to the number of physical lines over which data is sent simultaneously. A 32-wire ribbon cable can transmit 32 bits in parallel. The term "width" is used to refer to the number of bits that a bus can transmit at once. Additionally, the bus speed is also defined by its frequency (expressed in Hertz), the number of data packets sent or received per second. Each time that data is sent or received is called a cycle. This way, it is possible to find the maximum transfer speed of the bus, the amount of data which it can transport per unit of time, by multiplying its width by its frequency. A bus with a width of 16 bits and a frequency of 133 MHz, therefore, has a transfer speed equal to: 16 * 133.106 = 2128*106 bit/s, or 2128*106/8 = 266*106 bytes/s or 266*106 /1000 = 266*103 KB/s or 259.7*103 /1000 = 266 MB/s

Bus subassembly In reality, each bus is generally constituted of 50 to 100 distinct physical lines, divided into three subassemblies: •

The address bus (sometimes called the memory bus) transports memory addresses which the processor wants to access in order to read or write data. It is a unidirectional bus.

•

The data bus transfers instructions coming from or going to the processor. It is a bidirectional bus.

•

The control bus (or command bus) transports orders and synchonisation signals coming from the control unit and travelling to all other hardware components. It is a bidirectional bus, as it also transmits response signals from the hardware.

The primary buses There are generally two buses within a computer: •

the internal bus (sometimes called the front-side bus, or FSB for short). The internal bus allows the processor to communicate with the system's central memory (the RAM).

•

the expansion bus (sometimes called the input/output bus) allows various motherboard components (USB, serial, and parallel ports, cards inserted in PCI connectors, hard drives, CD-ROM and CD-RW drives, etc.) to communicate with one another. However, it is mainly used to add new

devices using what are called expansion slots connected to the input/outpur bus.

The chipset A chipset is the component which routes data between the computer's buses, so that all the components which make up the computer can communicate with each other. The chipset originally was made up of a large number of electronic chips, hence the name. It generally has two components: •

The NorthBridge (also called the memory controller) is in charge of controlling transfers between the processor and the RAM, which is way it is located physically near the processor. It is sometimes called the GMCH, forr Graphic and Memory Controller Hub.

•

The SouthBridge (also called the input/output controller or expansion controller) handles communications between peripheral devices. It is also called the ICH (I/O Controller Hub). The tem bridge is generally used to designate a component which connects two buses.

It is interesting to note that, in order to communicate, two buses must have the same width. The explains why RAM modules sometimes have to be installed in pairs (for example, early Pentium chips, whose processor buses were 64-bit, required two memory modules each 32 bits wide).

Here is a table which gives the specifications for the most commonly used buses: Standard

Bus width (bits) Bus speed (MHz) Bandwidth (MB/sec)

ISA 8-bit

8

8.3

7.9

ISA 16-bit

16

8.3

15.9

EISA

32

8.3

31.8

VLB

32

33

127.2

PCI 32-bit

32

33

127.2

PCI 64-bit 2.1

64

66

508.6

AGP

32

66

254.3

AGP (x2 Mode)

32

66x2

528

AGP (x4 Mode)

32

66x4

1056

AGP (x8 Mode)

32

66x8

2112

ATA33

16

33

33

ATA100

16

50

100

ATA133

16

66

133

Serial ATA (S-ATA)

1

180

Serial ATA II (S-ATA2)

2

380

USB

1

1.5

USB 2.0

1

60

FireWire

1

100

FireWire 2

1

200

SCSI-1

8

4.77

5

SCSI-2 - Fast

8

10

10

SCSI-2 - Wide

16

10

20

SCSI-2 - Fast Wide 32 bits 32

10

40

SCSI-3 - Ultra

8

20

20

SCSI-3 - Ultra Wide

16

20

40

SCSI-3 - Ultra 2

8

40

40

SCSI-3 - Ultra 2 Wide

16

40

80

SCSI-3 - Ultra 160 (Ultra

16

80

160

3) SCSI-3 - Ultra 320 (Ultra 4)

16

80 DDR

320

SCSI-3 - Ultra 640 (Ultra 5)

16

80 QDR

640

Computer - ISA, MCA and VLB Buses

NextPCI

Expansion Bus Expansion buses (sometimes called peripheral buses) are buses that have connectors that allow you to add expansion cards (peripherals) to a computer. There are different types of standard internal buses that are characterised by: •

their shape

•

the number of connector pins

•

the type of signals (frequency, data, etc.)

ISA Bus The original version of the ISA bus (Industry Standard Architecture) that appeared in 1981 with PC XT was an 8-bit bus with a clock speed of 4.77 MHz. In 1984, with the appearance of PC AT (the Intel 286 processor), the bit was expanded into a 16-bit bus and the clock speed went from 6 to 8 MHz and finally to 8.33 MHz, offering a maximum transfer rate of 16 Mb/s (in practice only 8 Mb/s because one cycle out of every two was used for addressing). The ISA bus permitted bus mastering, i.e. it enabled controllers connected directly to the bus to communicate directly with the other peripherals without going through the processor. One of the consequences of bus mastering is direct memory access (DMA). However, the ISA bus only allows hardware to address the first 16 megabytes of RAM. Up until the end of the 1990s, almost all PC computers were equipped with the ISA bus, but it was progressively replaced by the PCI bus, which offered a better performance. •

8-bit ISA Connector:

•

16-bit ISA Connector:

MCA Bus

The MCA bus (Micro Channel Architecture) is an improved proprietary bus designed by IBM in 1987 to be used in their PS/2 line of computer. This 16 to 32-bit bus was incompatible with the ISA bus and could reach a throughput of 20 Mb/s. EISA Bus The EISA bus (Extended Industry Standard Architecture) was developed in 1988 by a consortium of companies (AST, Compaq, Epson, Hewlett-Packard, NEC, Olivetti, Tandy, Wyse and Zenith) in order to compete with the MCA proprietary bus that was launched by IBM the previous year. The EISA bus used connectors that were the same size as the ISA connector but with 4 rows of contacts instead of 2, for 32-bit addressing. The EISA connectors were deeper and the additional rows of contacts were placed below the rows of ISA contacts. Thus, it was possible to plug an ISA expansion board into an EISA connector. However, they did not plug as deep into the connector (because of the bezels) and thus only used the top rows (ISA) of contacts. Local Bus Traditional I/O buses, such as ISA, MCA our EISA buses, are directly connected to the main bus and there are forced to work at the same frequency. However, some I/O peripherals need a very low bandwidth while other need higher bandwidths. Therefore there are bottlenecks on the bus. In order to solve this problem, the "local bus" architecture offers to take advantage of the system bus, or front side bus (FSB), by interfacing directly with it. VLB Bus In 1992, the VESA local bus (VLB) was developed by the VESA (Video Electronics Standard Association under the aegis of the company NEC) in order to offer a local bus dedicated to graphics systems. The VLB is a 16-bit ISA connector with an added 16-bit connector: The VLB bus is a 32-bit bus initially intended to work a bandwidth of 33 MHz (the bandwidth of the first PC 486s at that time). The VESA local bus was used on the following 486 models (40 and 50 MHz, respectively) as well as on the very first Pentium processors, but it was quickly replaced by the PCI bus. PCI Bus

NextAGP

The PCI Bus The PCI bus (Peripheral Component Interconnect) was developed by Intel on 22 June 1992. Contrary to the VLB bus, it is not so much a traditional local bus but rather an intermediate bus located between the processor bus (NorthBridge) and the I/O bus (SouthBridge). PCI Connectors At least 3 or 4 PCI connectors are generally present on motherboards and can generally be recognised by their standardised white colour. The PCI interface exists in 32 bits with a 124-pin connector, or in 64 bits with a 188pin connector. There are also two signalling voltage levels: •

3.3V, for laptop computers

•

5V, for desktop computers

The signalling voltage does not equal the voltage of the motherboard power supply but rather the voltage threshold for the digital encryption of data. There are 2 types of 32-bit connectors: •

32-bit PCI connector, 5V:

•

32-bit PCI connector, 3.3V:

The 64-bit PCI connectors offer additional pins and can accommodate 32-bit PCI cards. There are 2 types of 64-bit connectors: •

64-bit PCI connector, 5V:

•

64-bit PCI connector, 3.3V:

Interoperability Generally, it is not possible to make a mistake when plugging a PCI card into a PCI slot. If the card plugs in correctly, it is compatible. Otherwise, there are foolproof devices to keep you from installing it.

There are expansion boards that have what are called "universal" connectors, i.e. that have two types of foolproof devices (two notches). These expansion cards can detect signalling voltage and adapt to it, and can therefore can be inserted independantly in 3.3V or 5V slots. Bus Updates The original version of the PCI bus is 32-bits wide and has a clock speed of 33 MHz, which allows it to theoretically provide a throughput of 132 Mb/s on 32 bits. On 64-

bit architectures, the bus operates on 64 bits and offers a theoretical throughput of 264 Mb/s. An interest group made up of a large number of manufacturers, dubbed PCI-SIG (PCI Special Interests Group), was created to upgrade the PCI standard. Bus updates were published. Version 2.0 from 30 April 1993 defined the shape of the connectors and additional cards and gave it a clock speed of 66 MHz versus 33 MHz for version 1.0, therefore doubling its theoretical throughput to reach 266 Mb/s on 32 bits. On 1 June 1995, revision 2.1 of the PCI bus improved its use to 66 MHz. At the time, engineers anticipated a progressive move from 5V signalling voltage toward 3.3V. Version 2.2 of the PCI bus, which appeared on 18 December 1998, allowed peripherals to be plugged in when hot (hot plug). Revision 2.3, edited on 29 March 2002, did away with the possibility of using additional 5V cards but permitted the use of cards that support both voltages in order to ensure downward compatibility. Revision 3.0 of the PCI standard completely did away with the use of 5V compatible cards. In September 1999, a major change to the PCI bus was made, dubbed PCI-X. The PCI-X 1.0 bus supports 66, 100 and 133 MHz frequencies. The PCI-X bus is fully compatible with the PCI format. PCI-X slots support PCI format cards and vice versa. Revision 2.0 of the PCI-X bus supports 66, 100, 133, 266 and 533 MHz frequencies and allows throughputs of 4.27 Gb/s on 64 bits. The table below summarises the different PCI bus revisions: Revision Release Date Frequency Voltage

Width 32 bits 133 Mb/s

PCI 1.0

1992

33 MHz

Nil 64 bits 266 Mb/s 32 bits 132 Mb/s

PCI 2.0

1993

33 MHz

3.3V / 5V 64 bits 264 Mb/s 32 bits 132 Mb/s

33 MHz

3.3V / 5V 64 bits 264 Mb/s

PCI 2.1

1995 32 bits 264 Mb/s 66 MHz

3.3V 64 bits 528 Mb/s 32 bits 132 Mb/s

33 MHz

3.3V / 5V 64 bits 264 Mb/s

PCI 2.2

1998 32 bits 264 Mb/s 66 MHz

3.3V 64 bits 528 Mb/s 32 bits 132 Mb/s

33 MHz

3.3V / 5V 64 bits 264 Mb/s

PCI 2.3

2002 32 bits 264 Mb/s 66 MHz

3.3V 64 bits 528 Mb/s

PCI-X 1.0 1999

66 MHz

3.3V

32 bits 264 Mb/s 64 bits 528 Mb/s

32 bits 400 Mb/s 100 MHz 3.3V 64 bits 800 Mb/s 32 bits 532 Mb/s 133 MHz 3.3V 64 bits 1,064 Mb/s 32 bits 264 Mb/s 66 MHz

3.3V 64 bits 528 Mb/s 32 bits 400 Mb/s

100 MHz 3.3V 64 bits 800 Mb/s 32 bits 532 Mb/s PCI-X 2.0 2002

133 MHz 3.3V 64 bits 1,064 Mb/s 32 bits 1,064 Mb/s 266 MHz 3.3V / 1.5V 64 bits 2,128 Mb/s 32 bits 2,128 Mb/s 533 MHz 3.3V / 1.5V 64 bits 4,256 Mb/s

AGP bus

NextPCI Express

Introduction to the AGP bus The AGP bus (short for Accelerated Graphics Port) was released in May 1997 for Slot One chipsets, then was later released for Super 7 chips in order to manage graphical data flow, which had grown to large to be handled by a PCI bus. The AGP bus is directly linked to the processor's FSB (Front Side Bus) and uses the same frequency, for increased bandwidth. The AGP interface was developed specifically to connect with the video card, by opening a direct memory access (DMA) channel to the graphics board, bypassing the input-output controller. Cards which employ this graphics bus theoretically require less on-board memory; because they can directly access graphical data (such as textures) stored in central memory, their cost is hypothetically lower. Version 1.0 of the AGP bus, which used 3.3 V of power, had a 1X mode that could send 8 bytes every two cycles, and a 2x mode for transferring 8 bytes per cycle. In 1998, AGP version 2.0 added AGP 4X, which could send 16 bytes per cycle. Version 2.0 of AGP was powered by 1.5 V, and AGP 2.0 "universal" connectors which could support either voltage were released. AGP version 3.0, released in 2002, doubled the speed of AGP 2.0 with a new AGP 8x mode. Characteristics of AGP The AGP 1X port operates at 66 MHz, as opposed to 33 MHz for a PCI bus, giving it a top speed of 264 MB/s (vs. 132 MB/s, shared between all the cards, for PCI). This gives AGP better performance, especially when displaying complicated 3D scenes.

When AGP 4X was released, its speed went up to 1 GB/s. This generation of AGP used 25 W of power. The next generation was named AGP Pro and used 50W. AGP Pro 8x offers speeds of 2 GB/s. The transfer speeds for the various AGP standards are: •

AGP 1X: 66.66 MHz x 1(coef.) x 32 bits /8 = 266.67 MB/s

•

AGP 2X: 66.66 MHz x 2(coef.) x 32 bits /8 = 533.33 MB/s

•

AGP 4X: 66.66 MHz x 4(coef.) x 32 bits /8 = 1.06 GB/s

•

AGP 8X: 66.66 MHz x 8(coef.) x 32 bits /8 = 2.11 GB/s

It should be noted that each of these AGP standards is backwards-compatible, meaning that AGP 4X or AGP 2X cards can be inserted into an AGP 8X slot. AGP Connectors Recent motherboards are built with a general AGP connector which can be identified by its brown colour. There are three types of connectors: •

AGP 1.5 volt connector:

•

AGP 3.3 volt connector:

•

Universal AGP connector:

Summary Here is a table summarising the technical specifications for each version and mode of AGP: AGP

Voltage

Mode

AGP 1.0

3.3 V

1x, 2x

AGP 2.0

1.5 V

1x, 2x, 4x

AGP 2.0 universal 1.5 V, 3.3 V 1x, 2x, 4x

AGP 3.0

1.5 V

4x, 8x

PCI Express Bus (PCI-E)

NextSerial/parallel port

The PCI Express Bus The PCI Express bus (Peripheral Component Interconnect Express, written PCI-E or 3GIO for "Third Generation I/O"), is an interconnect bus that allows you to add expansion boards to a computer. The PCI Express bus was developed in July 2002. Contrary to the PCI bus, which runs in parallel interface, the PCI Express bus runs in serial interface, which allows it to reach a bandwidth that is much higher than that PCI bus.

Characteristics of the PCI Express Bus The PCI Express bus comes in several versions (1X, 2X, 4X, 8X, 12X, 16X and 32X), which provide throughputs of between 250 Mb/s and 8 Gb/s, or close to 4 times the peak throughput of AGP 8X ports. Because its manufacturing cost is that similar to that of the AGP port, the PCI Express bus will progressively replace the former. PCI Express Connectors PCI Express connectors are not compatible with older PCI connectors. They vary in size and require less electricity. One of the interesting characteristics of the PCI Express bus is that it is hot pluggable, i.e. it can be plugged in or unplugged with out turning off or restarting the machine. PCI Express connectors can be recognised thanks to their small size and dark grey colour. •

The PCI Express 1X connector has 36 pins and is intended for high-bandwidth I/O use

•

The PCI Express 4X connector has 64 pins and is intended to be used on servers:

•

The PCI Express 8X connector has 98 pins and is intended to be used on servers:

•

The PCI Express 16X connector has 164 pins, is 89 mm long and is intended to be used on the graphics port:

The PCI Express standard is also intended to replace PC Card technology with "PCI Express Mini Card" connectors. What is more, contrary to PCI connectors which can only be used for to make internal connections, the PCI Express standard can be used to connect external peripherals by using cables. Despite that fact, it is not in competition with USB or FireWire ports. Serial port and parellel port

NextUSB

Introduction to input-output ports Input-output ports are material elements on the computer, allowing the system to communicate with exterior elements, in other words to exchange data, hence the name input-output interface (sometimes known as I/O interface). Serial port Serial ports (also called RS-232, after the name of the standard they refer to) represent the first interfaces to allow computers to exchange information with the "outside world". The term serial refers to data sent via a single wire: the bits are sent one after the other (refer to section on data transmission for a presentation on transmission modes).

Serial ports were originally able to only send data and not receive it, hence two-way ports were developed (the ports on current computers are two-way); two-way serial ports therefore need two wires for communication. Serial communication takes place asynchronously, meaning that no synchronisation signal (or clock) is required: the data may be sent at random intervals. In return, the peripheral must be able to distinguish the characters (one character is 8 bits in length) among the succession of bits which is sent. This is why, in this type of transmission, each character is preceded by a START bit and followed by a STOP bit. These control bits, which are needed for serial transmission, waste 20% of the bandwidth (for 10 bits sent, 8 are used to code the character and 2 are used for reception).

Serial ports are generally built into the mother board, which is why the connectors behind the casing and connected to the mother board by a wire cable can be used to connect an exterior element. Serial connectors generally have 9 or 25 pins and take the following form (DB9 and DB25 connectors respectively):

A personal computer generally has between one and four serial ports. Parallel port Parallel data transmission involves sending data simultaneously on several channels (wires). The parallel ports on personal computers can be used to send 8 bits (one octet) simultaneously via 8 wires.

The first two-way parallel ports allowed for speeds of 2.4Mb/s. Enhanced parallel ports have been developed however to achieve higher speeds: •

The EPP (Enhanced Parallel Port) achieves speeds of 8 to 16 Mbps

•

The ECP (Enhanced Capabilities Port), developed by Hewlett Packard and Microsoft. It has the same characteristics as the EPP with in addition a Plug and Play feature, allowing the computer to recognise the connected peripherals.

Parallel ports, like serial ports, are built into the mother board. DB25 connectors allow connection to an exterior element (e.g. a printer).

The USB (Universal Serial Bus)

NextFireWire

Introduction to the USB USB (Universal Serial Bus) is as its name suggests, based on serial type architecture. However, it is an input-output interface much quicker than standard serial ports. Serial architecture was used for this type of port for two main reasons: •

Serial architecture gives the user a much higher clock rate than a parallel interface because a parallel interface does not support too high frequencies (in a high speed architecture, bits circulating on each wire arrive with lag, causing errors);

•

serial cables are much cheaper than parallel cables.

USB standards So, from 1995, the USB standard has been developed for connecting a wide range of devices. The USB 1.0 standard offers two modes of communication: •

12 Mb/s in high speed mode,

•

1.5 Mb/s in low speed.

The USB 1.1 standard provides several clarifications for USB device manufacturers but does not change anything in the speed. USB 1.1 certified devices carry the following logo:

The USB 2.0 standard makes it possible to obtain speeds which can reach 480 Mbit/s/ USB 2.0 certified devices carry the following logo:

If there is no logo, the best way of determining if something is a low or high speed USB is to consult the product documentation insofar as the connectors are the same. Compatibility between USB 1.0, 1.1 and 2.0 is assured. However, the use of a USB 2.0 device in a low speed USB port (i.e. 1.0 or 1.1) will limit the speed to 12Mbit/s maximum. Furthermore, the operating system is likely to display a message explaining that the speed will be restricted. Types of connectors There are two types of USB connectors: •

Connectors known as type A, where the shape is rectangular and generally used for less bandwidth intensive devices (keyboard, mouse, webcam, etc.);

•

Connectors known as type B, where the shape is square and mainly used for high speed devices (external hard disks, etc.);

1. 2. 3. 4.

Power supply +5V (VBUS) 100mA maximum Data (D-) Data (D+) Mass (GND)

Operation of the USB One characteristic of USB architecture is that it can supply electricity to devices to which it connects, with a limit of 15 W maximum per device. To do so, it uses a cable made up of four wires (the GND mass, the BUS supply and two data wires called Dand D+).

The USB standard allows devices to be chained by using a bus or star topology. So, devices can either be connected one to another or branched. Branching is done using boxes called "hubs" comprising of a single input and several outputs. Some are active (supplying electric energy), others passive (power supplied by the computer).

Communication between the host (computer) and devices is carried out according to a protocol (communication language) based on the token ring principle. This means that bandwidth is temporarily shared between all connected devices. The host (computer) issues a signal to begin the sequence every millisecond (ms), the time interval during which it will simultaneously give each device the opportunity to "speak". When the host wants to communicate with a device, it transmits a token (a data packet, containing the address of the device coded over 7 bits) designating a device, so it is the host that decides to "talk" with the devices. If the device recognises its address in the token, it sends a data packet (between 8 and 255 bytes) in response, if not it passes the packet to the other connected devices. Data is exchanged in this way is coded according to NRZI coding. Since the address is coded over 7 bits, 128 devices (2^7) can simultaneously be connected to a port of this type. In reality, it is advisable to reduce this number to 127 because the 0 address is a reserved address. (see later).

Due to the maximum length of the cable between two devices of 5 metres and a maximum number of 5 hubs (supplied), it is possible to create a chain 25 meters in length. USB ports support Hot plug and play. So, devices can be connected without turning off the computer (hot plug). When a device is connected to the host it detects the addition of a new item thanks to a change in the tension between the D+ and Dwires. At this time, the computer sends an initialisation signal to the device for 10ms, then it supplies the current using the GND and VBUS wires (up to 100mA). The device is then supplied with electric current and temporarily takes over the default address (0 address). The following stage consists of supplying it with its definitive address (this is the listing procedure). To do so, the computer interrogates devices already connected to know their addresses and allocates a new one, which identifies it by return. The host, having all the necessary characteristics is then able to load the appropriate driver. FireWire Bus (iLink / IEEE 1394) NextIDE / ATA

Presentation of FireWire Bus (IEEE 1394) The IEEE 1394 bus (name of the standard to which it makes reference) was developed at the end of 1995 in order to provide an interconnection system that allows data to circulate at a high speed and in real time. The company Apple gave it the commercial name "FireWire", which is how it is most commonly known. Sony also gave it commercial name, i.Link. Texas Instruments preferred to call it Lynx. FireWire is a port that exists on some computers that allows you to connect peripherals (particularly digital cameras) at a very high bandwidth. There are expansion boards (generally in PCI or PC Card / PCMCIA format) that allow you to equip a computer with FireWire connectors. FireWire connectors and cables can be easily spotted thanks to their shape as well as the following logo:

FireWire Standards There are different FireWire standards that allow you to obtain the following bandwidths: Standard

Theoretical Bandwidth

IEEE 1394a IEEE 1394a-S100 100 Mbit/s IEEE 1394a-S200 200 Mbit/s IEEE 1394a-S400 400 Mbit/s IEEE 1394b IEEE 1394b-S800 800 Mbit/s IEEE 1394b-S1200 1,200 Mbit/s IEEE 1394b-S1600 1,600 Mbit/s

IEEE 1394b-S3200 3,200 Mbit/s The IEEE 1394b standard is also called FireWire 2 or FireWire Gigabit. FireWire Connectors There are different FireWire connectors for each of the IEEE 1394 standards. •

The IEEE 1394a standard specifies two connectors: o

Connectors 1394a-1995:

o

Connectors 1394a-2000, called mini-DV because they are used on Digital Video (DV) cameras:

•

The IEEE 1394b standard specifies two types of connectors that are designed so that 1394b-Beta cables can be plugged into Beta and Bilingual connectors, but 1394b Bilingual cables can only be plugged into Bilingual connectors: o

1394b Beta connectors:

o

1394b Bilingual connectors:

How the FireWire Bus Works The IEEE 1394 bus has about the same structure as the USB bus except that it is a cable made up of six wires (2 pairs for the data and the clock and 2 wires for the power supply) that allow it to reach a bandwidth of 800 Mb/s (soon it should be able to reach 1.6 Gb/s, or even 3.2 Gb/s down the road). The two wires for the clock is the major difference between the USB bus and the IEEE 1394 bus, i.e. the possibility to operate in two transfer modes: •

Asynchronous transfer mode: this mode is based on a transmission of packets at variable time intervals. This means that the host sends a data packet and waits to receive a receipt notification from the peripheral. If the

host receives a receipt notification, it sends the next data packet. Otherwise, the first packet is resent after a certain period of time. •

Synchronous mode: this mode allows data packets of specific sizes to be sent in regular intervals. A node called Cycle Master is in charge of sending a synchronisation packet (called a Cycle Start packet) every 125 microseconds. This way, no receipt notification is necessary, which guarantees a set bandwidth. Moreover, given that no receipt notification is necessary, the method of addressing a peripheral is simplified and the saved bandwidth allows you to gain throughput.

Another innovation of the IEEE 1394 standard: bridges (systems that allow you to link buses to other buses) can be used. Peripheral addresses are set with a node (i.e. peripheral) identifier encoded on 16 bits. This identifier is divided into two fields: a 10-bit field that identifies the bridge and a 6-bit field that specifies the node. Therefore, it is possible to connect 1,023 bridges (or 210 -1) on which there can be 63 nodes (or 26 -1), which means it is possible to address 65,535 peripherals! The IEEE 1394 standard allows hot swapping. While the USB bus is intended for peripherals that do not require a lot of resources (e.g. a mouse or a keyboard), the IEEE 1394 bandwidth is larger and is intended to be used for new, unknown multimedia (video acquisition, etc.). ATA, IDE and EIDE NextSerial ATA

Overview The ATA (Advanced Technology Attachment) standard is a standard interface that allows you to connect storage peripherals to PC computers. The ATA standard was developed on May 12, 1994 by the ANSI (document X3.221-1994). Despite the official name "ATA", this standard is better known by the commercial term IDE (Integrated Drive Electronics) or Enhanced IDE (EIDE or E-IDE). The ATA standard was originally intended for connecting hard drives, however an extension called ATAPI (ATA Packet Interface) was developed in order to be able to interface other storage peripherals (CD-ROM drives, DVD-ROM drives, etc.) on an ATA interface. Since the Serial ATA standard (written S-ATA or SATA) has emerged, which allows you to transfer data over a serial link, the term "Parallel ATA" (written PATA or PATA) sometimes replaces the term "ATA" in order to differentiate between the two standards. The Principle The ATA standard allows you to connect storage peripherals directly with the motherboard thanks to a ribbon cable, which is generally made up of 40 parallel wires and three connectors (usually a blue connector for the motherboard and a black connector and a grey connector for the two storage peripherals).

On the cable, one of the peripherals must be declared the master cable and the other the slave. It is understood that the far connector (black) is reserved for the master peripheral and the middle connector (grey) for the slave peripheral. A mode called cable select (abbreviated as CS or C/S) allows you to automatically define the master and slave peripherals as long as the computer's BIOS supports this functionality. PIO Modes Data transmission occurs thanks to a protocol called PIO (Programmed Input/Output), which allows peripherals to exchange data with the RAM with the help of commands managed directly by the processor. However, large data transfers can quickly impose a large workload on the processor and slow down the whole system. There are 5 PIO modes that define the maximum throughput:

PIO Mode Throughput (Mb/s) Mode 0

3.3

Mode 1

5.2

Mode 2

8.3

Mode 3

11.1

Mode 4

16.7

DMA Modes The DMA (Direct Memory Access) technique allows computers to free up the processor by allowing each of the peripherals to directly access the memory. There are two types of DMA modes: •

The "single word" DMA, which permits the transfer of one single word (2 bytes or 16 bits) during each transfer session

•

The "multi-word" DMA, which permits the successive transfer of several words in each transfer session

The following table lists the different DMA modes and their associated throughputs:

DMA Mode

Throughput (Mb/s)

0 (Single word) 2.1 1 (Single word) 4.2 2 (Single word) 8.3 0 (Multi-word) 4.2 1 (Multi-word) 13.3 2 (Multi-word) 16.7

Ultra DMA The ATA standard is originally based on an asynchronous transfer mode, i.e. sending commands and sending data are clocked to the bandwidth of the bus and occur at each rising edge of the clock signal. However, sending commands and sending data do not occur simultaneously, i.e. a command cannot be sent as long as the data has not been received and vice versa. In order to increase the data throughput, it may seem logical to increase the clock signal frequency. However, on an interface where data are sent in parallel, increasing the frequency poses problems of electromagnetic interference. Thus, Ultra DMA (sometimes abbreviated as UDMA) was designed with the goal of optimising the ATA interface as much as possible. The first concept of Ultra DMA consists in using the rising edges as well as the falling edges of the signal for the data transfers, meaning an increase in speed of 100% (with the throughput increasing from 16.6 Mb/s to 33.3 Mb/s). Moreover, Ultra DMA introduces the use of CRC codes for the detection of transmission errors. Thus, the different Ultra DMA modes define the frequency of data transfer. When an error occurs (when the received CRC does not correspond to the data), the transfer occurs in a lower Ultra DMA mode, or even without Ultra DMA.

Ultra DMA Mode

Throughput (Mb/s)

UDMA 0

16.7

UDMA 1

25.0

UDMA 2 (Ultra-ATA/33) 33.3 UDMA 3

44.4

UDMA 4 (Ultra-ATA/66) 66.7 UDMA 5 (UltraATA/100)

100

UDMA 6 (UltraATA/133)

133

With the introduction of Ultra DMA mode 4, a new type of cable ribbon was introduced in order to limit crosstalk. This type of ribbon cable adds 40 wires (for a total of 80) that are interleaved with the data wires in order to isolate them and have the same connectors as the 40-wire cable ribbon.

Only Ultra DMA modes 2, 4, 5 and 6 are truly implemented by hard drives. ATA Standards The ATA standard comes in several versions, which were introduced successively: ATA-1 The ATA-1 standard, better known as IDE, allows you to connect two peripherals on a 40-wire cable and offers an 8 or 16-bit transfer rate with a throughput of the order of 8.3 Mb/s. ATA-1 defines and supports PIO modes (Programmed Input/Output) 0, 1 and 2 as well as multi-word DMA mode (Direct Memory Access) 0. ATA-2 The ATA-2 standard, better known as EIDE (or sometimes Fast ATA, Fast ATA-2 or Fast IDE), allows you to connect two peripherals on a 40-wire cable and offers an 8 or 16-bit transfer rate with a throughput of the order of 16.6 Mb/s. ATA-2 supports PIO modes 0, 1, 2, 3 and 4 and multi-word DMA modes 0, 1 and 2. In addition, ATA-2 allows you to increase the maximum disk size from 528 Mb, which is imposed by the ATA-1 standard, to 8.4 Gb thanks to LBA (Large Block Addressing). ATA-3 The ATA-3 standard (also called ATA Attachment 3 Interface) represents a minor revision of ATA-2 (with downward compatibility) and was published in 1997 under the standard X3.298-1997. The ATA-3 standard brings the following improvements: •

Improved reliability: ATA-3 enables the increased reliability of high-speed transfers

•

S.M.A.R.T (Self-Monitoring Analysis and Reporting Technology: a function intended to improve reliability and prevent against failures

•

Security function: the peripherals can be protected by a password added to the BIOS. When the computer is started, it verifies that the password encoded in the BIOS corresponds to the one stored on the drive. This allows you to prevent the drive from being used on a different computer.

ATA-3 is not a new mode but supports PIO modes 0, 1, 2, 3 and 4 as well as DMA modes 0, 1 and 2. ATA-4 The ATA-4 standard, or Ultra-ATA/33, was defined in 1998 under the standard ANSI NCITS 317-1998. ATA-4 modifies the LBA mode in order to increase the disk size limit to 128-Gb drives. LBA addresses in ATA-4 are 28-bit. Each sector represents 512 bytes, so the exact disk size limit in LBA mode is as follows: 228*512 = 137 438 953 472 bytes 137 438 953 472/(1024*1024*1024)= 128 Gb

ATA-5 In 1999, the ATA-5 standard defined two new transfer modes: Ultra DMA modes 3 and 4 (mode 4 is also called Ultra ATA/66 or Ultra DMA/66). What is more, it offers automatic detection of the type of ribbon cables being used (80 or 40 wires). ATA-6 Since 2001, ATA-6 defines Ultra DMA/100 (also called Ultra DMA mode 5 or UltraATA100), which allows drives to theoretically reach throughputs of 100 Mb/s. In addition, ATA-6 defines a new functionality, called Automatic Acoustic Management (AAM), which allows drives that support this function to automatically adjust access speeds in order to reduce running noise. Finally, the ATA-6 standard allows a 48-bit LBA of the sectors of the hard drive, called LBA48 (Logical Block Addressing 48 bits). Thanks to LBA48, it is possible to use 2^48 hard drives with 512 bytes per sector, which equals a disk size limit of 2 petabytes. ATA-7 The ATA-7 standard defines Ultra DMA/133 (also called Ultra DMA mode 6 or Ultra-ATA133), which allows drives to theoretically reach throughputs of 133 Mb/s. Summary Table Name

ATA-1

ANSI Standard

Synonym

ANSI IDE X3.221-1994

Mode Throughput (PIO/DMA) (Mb/s) PIO mode 0

3,3

PIO mode 1

5,2

PIO mode 2

8,3

Comments

DMA mode 0 8,3 ATA-2

ANSI

EIDE, Fast ATA, PIO mode 3

11,1

28-bit LBA

PIO mode 4 X3.279-1996 Fast ATA-2

16,7

DMA mode 1 13,3 DMA mode 2 16,7

ATA-3

ANSI X3.298-1997

PIO mode 3

11,1

PIO mode 4

16,7 SMART, 28-bit LBA

DMA mode 1 13,3 DMA mode 2 16,7 UDMA mode 16,7 0

Ultra-ATA/33, ATAANSI NCITS UDMA 33, Ultra 4/ATAPI-4 317-1998 DMA 33

UDMA mode 25,0 1

Ultra DMA 33 and supports CD-ROMs (ATAPI)

UDMA mode 33,3 2 UDMA mode 44,4 3 Ultra-ATA/66, ATAANSI NCITS UDMA 66, Ultra 5/ATAPI-5 340-2000 DMA 66 UDMA mode 66,7 4

Ultra DMA 66, uses a 80-wire cable

Ultra-ATA/100, ATAANSI NCITS UDMA mode UDMA 100, Ultra 100 6/ATAPI-6 347-2001 5 DMA 100

Ultra DMA 100, LBA48 and the AAC (Automatic Acoustic Management) function

Ultra-ATA/133, ATAANSI NCITS UDMA mode UDMA 133, Ultra 133 7/ATAPI-7 361-2002 6 DMA 133

Ultra DMA 133

Serial ATA (SATA or S-ATA)

NextSCSI

Introduction The Serial ATA standard (S-ATA or SATA) is a standard bus allowing high-speed storage peripherals to be connected to PC computers. The Serial ATA standard was introduced in February 2003 in order to compensate for limitations of the ATA standard (better known by the name "IDE" and retroactively called Parallel ATA), which uses a parallel transmission mode. Indeed, the parallel transmission mode is not designed to work with high frequencies due to problems related to electro-magnetic disturbances between the different wires. The S-ATA standard cables and peripherals can be identified by the presence of the following logo:

Principle of the Serial ATA The Serial ATA standard is based on serial communication. A data path is used to transmit the data and another path is used to transmit acknowledgements of receipt. On each of these data paths, data are transmitted via the LVDS (Low Voltage Differential Signalling) transmission mode which involves transferring a signal to a wire and its opposite to a second wire to allow the receiver to recreate the signal by difference. The control data are transmitted on the same path as the data using a specific sequence of bits to distinguish them. Thus the communication requires two transmission paths, each one comprising two wires, with a total of four wires used for the transmission. Serial-ATA connectors The cable used by the Serial ATA is a round cable containing 7 wires and with an 8mm connector on the end:

Three wires are grounded and two pairs are used to transmit data. The supply connector is also different: it comprises 15 pins which supply the peripheral with 3.3V, 5V or 12V power and looks similar to the data connector:

Technical characteristics The Serial ATA offers speeds of 187.5 Mo/s (1.5 Gb/s), and each octet is transmitted with a start bit and a stop bit, with a theoretical effective speed of 150 Mo/s (1.2 Gb/s). The Serial ATA II standard should help achieve 375 Mo/s (3 Gb/s), i.e. theoretical effective speed of 300 Mo/s, then finally 750 Mo/s (6 Gb/s), i.e. theoretical effective speed of 600 Mo/s. Serial ATA cables can measure up to 1 metre in length (compared with 45cm for IDE cables). Furthermore, the low number of wires in a round casing allows greater flexibility and better circulation of air in the casing than with IDE cables (even if round IDE cables exist). Contrary to the ATA standard, Serial ATA peripherals are alone on each cable and "master peripherals" and "slave peripherals" no longer need to be defined. Moreover, the Serial ATA standard allows for Hot Plugging). SCSI NextPC Card (PCMCIA)

Introduction to the SCSI interface The SCSI standard (Small Computer System Interface) is an interface used to connect several different types of peripherals to a computer via a card, known as the SCSI adaptor or SCSI controller (generally connected using a PCI connector). The number of peripherals that can be connected depends on the width of the SCSI bus. With an 8-bit bus, 8 physical units can be connected and 16 for a 16-bit bus. Since the SCSI controller represents a separate physical unit, the bus can therefore accommodate 7 (8-1) or 15 (16-1) peripherals. Addressing of peripherals Peripherals are addressed using identification numbers. The first number is the ID, which is a number designating the controller built into each peripheral (this is

defined via the jumpers to be positioned on each SCSI peripheral or by the software). The peripheral may have up to 8 logical units (e.g. a CD-ROM drive with several drawers). The logical units are identified by a LUN (Logical Unit Number). Lastly, a computer may contain several SCSI cards and therefore a card number is assigned to each of them. Thus, to communicate with a peripheral, the computer must give an address in the following form: "card number - ID - LUN". Asymmetrical and differential SCSI There are two types of SCSI bus: •

the asymmetrical bus, known as SE (for Single-Ended), based on a parallel architecture in which each channel circulates on one wire, making it sensitive to interference. The SCSI cables in SE mode have 8 wires for 8-bit transmission (and are known as narrow), or 16 wires for a 16-bit cable (known as wide). This is the most common type of SCSI bus.

•

the differential bus carries signals to a pair of wires. The information is coded by difference between the two wires (each conveying the opposing voltage) in order to offset the electro-magnetic disturbances, which allows a considerable cabling distance (of around 25 metres). Generally speaking, there are two modes: LVD mode (Low Voltage Differential), based on 3.3V signals and HVD mode (High Voltage Differential), using 5V signals. Peripherals using this type of transmission are rarer and generally bear the word "DIFF".

The connectors for the two peripheral categories are the same but the electrical signals are different. Therefore the peripherals need to be identified (using the symbols created for the purpose) so as not to damage them! SCSI standards The SCSI standards define the electrical parameters of the input/output interfaces. The SCSI-1 standard of 1986 defined the standard commands for controlling the SCSI peripherals on a bus with a frequency of 4.77 MHz with width of 8 bits, meaning that speeds of 5 Mo/s can be achieved. However, a large number of these commands were optional, thus in 1994 the SCSI2 standard was adopted. It defines 18 commands known as CCS (Common Command Set). Various versions of the SCSI-2 standard have been defined: •

The Wide SCSI-2 is based on a bus with 16 bits (instead of 8) and offers speed of 10 Mo/s

•

The Fast SCSI-2 is a rapid synchronous mode allowing an increase from 5 to 10 Mo/s for the standard SCSI and from 10 to 20 Mo/s for the Wide SCSI-2 (referred to as the Fast Wide SCSI-2)

•

The Fast-20 and Fast-40 modes respectively double and quadruple these speeds.

The SCSI-3 standard includes new commands and allows chaining of 32 peripherals and a maximum speed of 320 Mo/s (in Ultra-320 mode). The following table summarises the characteristics of the various SCSI standards: Standard

Bus width Bus speed

Bandwidth Connector

SCSI-1 (Fast-5 SCSI)

8 bits

4.77 MHz

5 MB/sec

50 pins (asymmetrical or differential bus)

SCSI-2 - Fast-10 SCSI

8 bits

10 MHz

10 MB/sec

50 pins (asymmetrical or differential bus)

SCSI-2 - Wide

16 bits

10 MHz

20 MB/sec

50 pins (asymmetrical or differential bus)

SCSI-2 - Fast Wide 32 bits

32 bits

10 MHz

40 MB/sec

68 pins (asymmetrical or differential bus)

SCSI-2 - Ultra SCSI-2 (Fast-20 SCSI)

8 bits

20 MHz

20 MB/sec

50 pins (asymmetrical or differential bus)

SCSI-2 - Ultra Wide SCSI-2

16 bits

20 MHz

40 MB/sec

SCSI-3 - Ultra-2 SCSI (Fast-40 SCSI)

8 bits

40 MHz

40 MB/sec

SCSI-3 - Ultra-2 Wide SCSI

16 bits

40 MHz

80 MB/sec

68 pins (differential bus)

SCSI-3 - Ultra-160 (Ultra-3 SCSI or Fast-80 SCSI)

16 bits

80 MHz

160 MB/sec

68 pins (differential bus)

SCSI-3 - Ultra-320 16 bits (Ultra-4 SCSI or Fast-160 SCSI)

80 MHz DDR 320 MB/sec

68 pins (differential bus)

SCSI-3 - Ultra-640 (Ultra-5 SCSI)

80 MHz QDR 640 MB/sec

68 pins (differential bus)

16

The PC Card bus (PCMCIA)

NextPeriphery Equipment

PC Card Bus Introduction The PC Card bus was developed in 1989 by the PCMCIA (Personal Computer Memory Card International Association, which is the name sometimes given to the bus) consortium in order to extend current peripheral equipment connectivity on mobile computers. Technical Characteristics PCMCIA peripheral equipment comes in the shape of a credit card (54mm by 85 mm) and has a 68-pin connector.

There are three form factors that correspond to three standard thicknesses:

Type

Width (mm) Length (mm) Thickness (mm)

Type I PC Card 54

85

3.3

Type II PC Card 54

85

5.0

Type III PC Card

85

10.5

54

Type I cards are generally used as memory expansion cards. Type II cards are generally for peripheral communication equipment (modem, network card, wireless network card) and small hard drives. Type III cards, much thicker, are generally used for peripheral equipment with mechanical elements (large capacity hard drives). CardBus Starting in 1995, the CardBus standard (sometimes called 32-bit PC Card) appeared, allowing 32-bit data transfer at a speed of 33 MHz with a 3V charge (versus 5.5 for PCMCIA). Periphery Equipment

NextHardware Interrupts (IRQ/DMA)

Periphery Equipment Concepts "Periphery equipment" is electronic equipment that can be plugged into a computer using one of its input/output interfaces (serial port, parallel port, USB bus, FireWire bus, SCSI interface, etc.), most often by using a connector. Periphery equipment is therefore external computer components. Periphery equipment is generally grouped into the following categories: •

display periphery equipment: output periphery equipment that provides a visual representation to the user, such as a monitor;

•

storage periphery equipment: input/output periphery equipment that can permanently store data (hard disk, CD-ROM, DVD-ROM, etc.);

•

capture periphery equipment: allows the computer to receive specific data such as video data, referred to as video capture or scanned images (scanner);

•

input periphery equipment: periphery equipment only capable of sending information to a computer, for example pointing devices (mouse) or the keyoard.

Expansion cards An "expansion card" is electronic hardware in card form that can be plugged into a computer using an expansion connector (ISA, PCI, AGP, PCI Express, etc.). Expansion cards are components that are connected directly to the motherboard and are located in the main unit, giving the computer new input-output functions. The main types of expansion cards are: •

graphic cards;

•

sound cards;

•

network cards;

Hardware Interrupts (IRQ) and Conflicts

NextScreen/Monitor

The Concept of Interrupts Because the processor cannot simultaneously process several pieces of information (it processes one piece of information at a time), a program being run can, thanks to an interrupt request, be momentarily suspended while an interrupt takes place. The interrupted program can then continue running. There are 256 different interrupt addresses. An interrupt becomes a hardware interrupt when it is requested by one of the computer's hardware components. There are many peripherals in a computer. These peripherals generally need to use the system resources if only to communicate with the system itself. When a peripheral wants to access a resource, it sends an interrupt request to the processor in order to get its attention. The peripherals have an interrupt number that is called an IRQ (Interruption ReQuest. It is as if each peripheral pulls a "string" that is attached to a bell in order to tell the computer that it wants the computer to pay attention to it. This "string" is in fact a physical line that links each expansion slot as well as each I/O interface to the motherboard. For an 8-bit ISA slot, for example, there are 8 IRQ lines that link the 8-bit ISA slots to the motherboard (IRQ0 to IRQ7). These IRQs are controlled by an "interrupt controller" that is in charge of allowing the IRQ with the greatest priority "to speak". When 16-bit slots were introduced, IRQs 8 to 15 were added, as was a second interrupt controller. The two groups of interrupts are linked by IRQ 2 which is connected (or "cascaded") to IRQ 9. In a way, this cascade "inserts" IRQs 8 to 15 between IRQs 1 and 3:

Given that priority goes from lowest to highest IRQ, and IRQs 8 to 15 are inserted between IRQs 1 and 3, the order of priority is as follows: 0 > 1 > 8 > 9 > 10 > 11 > 12 > 13 > 14 > 15 > 3 > 4 > 5 > 6 > 7 DMA The peripherals regularly need to "borrow memory" from the system in order to use it as a buffer zone, i.e. a temporary storage area that allows I/O data to be quickly saved. Thus, a direct memory access channel, called a DMA (Direct Memory Access was defined as a solution to this. The DMA channel indicates an access to one of the computer's random access memory (RAM) slots, located by a "RAM Start Address" and an "end address". This method allows a peripheral to borrow special channels that give it direct access to the memory, without the intervention of the microprocessor, in order to unload these tasks. A PC has 8 DMA channels. The first four DMA channels have an 8-bit bandwidth while DMAs 4 to 7 have a 16-bit bandwidth. The DMA channels are generally assigned as follows: •

DMA0 - free

•

DMA1 - (sound card)/ free

•

DMA2 - floppy disk controller

•

DMA3 - parallel port (printer port)

•

DMA4 - direct memory access (DMA) controller (connected to DMA0)

•

DMA1 - (sound card)/ free

•

DMA6 - (SCSI)/ free

•

DMA7 - available

Base Addresses Sometimes peripherals need to exchange information with the system, which is why memory addresses were assigned to them for the sending and receiving of data. These addresses are called "base addresses" (the following terms are also sometimes used: "input/output ports", "I/O ports", "I/O addresses", "I/O port addresses", or "base ports"). It is by using this base address that the peripheral can communicate with the operating system. Therefore, there is only one unique base address for each peripheral. Here is a list of some common base addresses: •

060h - keyboard

•

170h/376h - secondary IDE controller

•

1F0h/3F6h - primary IDE controller

•

220h - sound card

•

300h - network card

•

330h - SCSI adapter card

•

3F2h - disk drive controller

•

3F8h - COM1

•

2F8h - COM2

•

3E8h - COM3

•

2E8h - COM4

•

378h - LPT1

•

278h - LPT2

However, all of these elements are user-transparent, i.e. users do not have to worry about them. Hardware Conflicts An interrupt is a line that links the peripheral to the processor. An interrupt is a hardware interrupt when it is requested by one of the PC's hardware components. For example, this is the case when a key is touched and the keyboard wants to get the processor's attention for this event. However, all 256 interrupts cannot be requested as hardware interrupts and different peripherals always make very specific interrupts. Thus, when expansion boards are installed, you must make sure during configuration that the same interrupt is not used for two different peripherals. If this were to happen, a "hardware conflict" would occur and neither peripheral would function. Indeed, if two peripherals use the same interrupt, the system will not know how to distinguish between them. A hardware conflict does not only occur when two peripherals have the same hardware. A conflict can also occur when two peripherals have the same I/O address or use the same DMA channels. IRQ Configuration The IRQ of an expansion board can be modified in order to assign it an IRQ number that is not being used by another peripheral. •

On older peripherals, this IRQ number is attached to jumpers that are on the board.

•

On recent boards (that have a BIOS Plug & Play), resource (IRQ, DMA, I/O addresses) parametering is automatic. It can also be carried out by the OS or with the help of utilities provided with the expansion board. The plug & play mode must sometimes be deactivated in order to be able to modify the parameters manually.

It is still not easy to find available resources for all peripherals. Here then is a nonexhaustive list of resources that are generally used, which therefore cannot be assigned manually: IRQ Peripheral 0

Internal Clock

1

keyboard

2

programmable interrupt controller Cascade to IRQs 8 to 15

3

COM2/COM4 communications port

4

COM1/COM3 communications port

5

free

6

floppy disk controller

7

LPT1 printer port

8

CMOS (Real-time clock)

9

free

10

free

11

free

12

PS2 mouse port/free

13

numeric data processor (math coprocessor)

14

primary hard drive controller (IDE)

15

secondary hard drive controller (IDE) The COM1 and COM4 ports as well as the COM2 and COM3 ports use the same interrupts. This may seem illogical in that the same interrupt cannot be used by two peripherals. In reality, it is possible to use the COM1 port as well as the COM4 port (as well as the COM2 port and the COM3 port) so long as the are not active at the same time. Otherwise, the computer might freeze or function abnormally.

Resolving Hardware Conflicts If you have a hardware problem, first try to isolate the problem in order to determine which peripheral is causing the problem. This means that you must attempt to eliminate as many variables as possible until you discover which element is responsible: •

by opening the computer casing and removing one by one the elements that might have caused the conflict

•

by deactivating the software in the OS in order to deactivate the peripherals

Computer screen or monitor

NextCathode Ray Tube

Introduction to computer monitors A monitor (or screen) is a computer display unit. There are generally said to be two families of monitors:

•

Cathode-ray tube monitors (or CRT for short), which are used with most desktop computers. They are heavy and voluminous, and use a great deal of electricity.

•

Flat-screen monitors are used with most laptop computers, personal digital assistants (PDAs), and digital cameras, as well as an increasing number of desktop computers. These monitors are thinner (hence the name), light, and are less power-consuming.

Technical specifications The most common specifications for monitors are: •

Definition: the number of pixels that the screen can display. This number is usually between 640x480 (640 pixels long, 480 pixels wide) and 2048x1536, but higher resolutions are technically possible. The table below gives recommended definitions based on the size of the screen's diagonal:

Diagonal Definition 15

800x600

17

1024x768

19

1280x1024

21

1600x1200

•

The size: This is calculated by measuring the screen's diagonal, and is expressed in inches (an inch is about 2.54 cm). Be careful not to confuse a screen's definition with its size. After all, a screen of a given size can display different definitions, although in general screens which are larger in size have a higher definition. The standard screen sizes are as follows (this list is nonexhaustive):

•

o

14 inches, a diagonal of about 36 cm;

o

15 inches, a diagonal of about 38 cm;

o

17 inches, a diagonal of about 43 cm;

o

19 inches, a diagonal of about 48 cm;

o

21 inches, a diagonal of about 53 cm.

The dot pitch: This is the distance between two phosphors; the smaller it is, the more precise the image is. A dot pitch equal to or less than 0.25 mm will be comfortable to use, while monitors with a dot pitch equal to or greater than 0.28 mm should be avoided.

•

The resolution: This determines the number of pixels per surface unit (given in linear inches). This is abbreviated DPI, for Dots Per Inch. A resolution of 300 dpi means 300 columns and 300 rows of pixels per square inch, which means that there are 90,000 pixels per square inch. By comparison, a resolution of 72 dpi means that one pixel is 1"/72 (one inch divided by 72) or 0.353 mm, which corresponds to one pica (a typographical unit).

Graphics modes The term graphics mode refers to how information is displayed on the screen, in terms of definition and number of colours. It represents the ability of the graphics card to handle details, or the ability of the monitor to display them. MDA The MDA (Monochrome Display Adapter), which appeared in 1981, was the display mode for monochrome monitors, which could display text in 80 columns and 25 rows. This mode could only display ASCII characters. CGA CGA (color graphic adapter) mode appeared in 1981 shortly after MDA, with the release of the PC (personal computer). This graphics mode included: •

improved text mode display, with the ability to display characters in 4 colours

•

graphics mode display which could show pixels in 4 colours with a resolution of 320 pixels by 200 pixels (320x200)

EGA EGA (Enhanced Graphic Adapter) mode was released in early 1985. It could display 16 colours with a resolution of 640 by 350 pixels (640x350), much finer graphics than were possible in CGA mode. VGA VGA (Video Graphics Array) mode appeared in 1987. It offered a resolution of 720x400 in text mode and a resolution of 640 by 480 (640x480) in 16-colour graphics mode. It could also display 256 colours with a definition of 320x200 (a mode also known as MCGA for Multi-Colour Graphics Array). The VGA quickly became the baseline display mode for PCs. XGA In 1990, IBM introduced XGA (eXtended Graphics Array). Version 2 of this display mode, dubbed XGA-2, offered a resolution of 800x600 in 16 million colours and 1024x768 in 65536 colours.

SVGA SVGA (Super Video Graphics Array) is a graphics mode which can display 256 colours at resolutions of 640x200, 640x350 and 640x480. SVGA can also display higher definitions such as 800x600 or 1024x768 by using fewer colours. VESA In order to make up for the lack of standardisation in graphics modes, a consortium of major graphics card manufacturers was created (the VESA, Video Electronic Standard Association) in order to develop graphical standards. SXGA The SXGA (Super eXtended Graphics Array) standard, defined by the VESA consortium, refers to a resolution of 1280x1024 with 16 million colours. This mode is characterised by a screen ratio of 5:4, unlike the other modes (VGA, SVGA, XGA, UXGA). UXGA UXGA mode (Ultra eXtended Graphics Array) uses a resolution of 1600 x 1200 with 16 million colours. WXGA WXGA mode (Wide eXtended Graphics Array) uses a resolution of 1280 x 800 with 16 million colours. WSXGA WSXGA mode (Wide eXtended Graphics Array) uses a resolution of 1600 x 1024 with 16 million colours. WSXGA+ WSXGA+ mode (Wide Super eXtended Graphics Array+) uses a resolution of 1680 x 1050 with 16 million colours. WUXGA WUXGA mode (Wide eXtended Graphics Array) uses a resolution of 1920 x 1200 with 16 million colours. QXGA QXGA mode (Wide eXtended Graphics Array) uses a resolution of 2048 x 1536 with 16 million colours. QSXGA QSXGA mode (Wide eXtended Graphics Array) uses a resolution of 2560 x 2048 with 16 million colours. QUXGA QUXGA mode (Ultra eXtended Graphics Array) uses a resolution of 32000 x 2400 with 16 million colours.

Summary The table below summarizes the various resolutions, as well as the corresponding ratios: Display format Horizontal resolution Vertical resolution Number of pixels Ratio VGA

640

480

307,200

1

SVGA

800

600

480,000

1.56

XGA

1024

768

786,432

2.56

SXGA

1280

1024

1,310,720

4.27

SXGA+

1400

1050

1,470,000

4.78

SXGA+

1280

1024

1,310,720

4.27

UXGA

1600

1200

1,920,000

6.25

QXGA

2048

1536

3,145,728

10.2

QSXGA

2560

2048

5,242,800

17.1

QUXGA

3200

2400

7,680,000

25

Energy and radiation standards There are numerous standards for guaranteeing monitor quality, as well as to assure the consumer that the machine has been designed so as to limit radiation from electrostatic waves and to reduce energy consumption. In the late 80s, the standard MPR1 was created by the Swedish testing authority in order to measure the radiation emitted by hardware that gives off electrostatic waves. This standard was amended in 1990 to produce MPR2, which is recognised internationally. In 1992, the Swedish Confederation of Professional Employees introduced the TCO standard, which describes radiation emission levels not in terms of minimum safety levels, but in terms of the minimum technically achievable level. The TCO standard was revised in 1992, 1995 and 1999, resulting in the TCO92, TCO95 and TCO99 standards, respectively.

In 1993, a consortium of computer component manufacturers (VESA — Video Electronics Standards Association) created the standard DPMS (Display Power Management Signaling), which offered 4 operating modes for devices which conformed to it: •

On.

•

Standby, with power consumption lower than 25W.

•

Suspended, with power consumption lower than 8W. In this mode the electron gun is shut off, which means that the recovery time is longer than for standby.

•

Off.

Cathode Ray Tube monitor (CRT)

NextLCD/Plasma

Cathode ray tube monitor Most monitors (computer screens) use cathode ray tubes (or CRT for short), which are glass vacuum tubes into which an electron gun emits a flow of electrons guided by an electrical field towards a screen covered in small phosphorescent elements.

The electron gun is made up of a cathode, a negatively charged metallic electrode, and one or more anodes (positively charged electrodes). The cathode emits the electrons attracted by the anode. The anode acts as an accelerator and concentrator for the electrons, forming a flow of electrons aimed at the screen. A magnetic field guides the electrons from left to right and from top to bottom. It is created with two electrified X and Y plates (called deflectors) which send the flow horizontally and vertically, respectively.

The screen is covered with a fine layer of phosphorescent elements, called phosphors, which emit light by excitation when electrons strike them, creating a litup dot called a pixel. Activating the magnetic field causes the electrons to follow a scan pattern, going from left to right and then down to the next row once they reach the end.

The human eye cannot see this scanning due to persistence of vision. Try waving your hand in front of your screen to view the phenomenon: You'll see several hands at once! Combined with the firing and non-firing of the electron gun, scanning tricks your eyes into believing that only some pixels on the screen are lit up.

The colour monitor A black and white monitor can display different tones (shades of gray) by varying the intensity of the flow. For colour monitors, three electron beams (coming from three different cathodes) each strike a point with a specific colour: red, green, and blue (RGB). Three points of colour are called a triad (or dot trio). Blue phosphors use zinc sulfide, while green ones use zinc sulfide and cadmium sulfide. The red ones are hard to create, and are made from a mixture of yttrium and europium, or gadolinium oxide. However, these phosphors are so close together than the eye cannot separate them enough to tell them apart; it sees a single colour made up of these three colours. Try flicking a tiny drop of water onto the glass of your monitor: It will magnify the phosphors so that you can see them. What's more, to avoid smearing (such as an electron meant to strike a green phosphor colliding with blue instead), a metallic grid called the shadow mask is placed in front of the phosphoric layer to guide the electron flow. There are several different categories of CRT monitors, which are set apart by the mask used: •

FST-Invar (Flat Square Tube), whose phosphors are round. These monitors use a grid called a shadow mask. They give the right colours overall, but have the disadvantage of distorting and darkening the image at the corners.

•

Mitsubishi's Diamondtron tubes and Sony's Trinitron, whose masks are made up of vertical slots (called an aperture grille or tension mask), which lets through more electrons and therefore gives a brighter image.

•

Nec's Cromaclear tubes, whose mask is uses of a hybrid system with dimpled slots, is the best technology of the three.

Technical specifications

The specifications for CRT monitors include: •

The definition: The number of pixels that the screen can display. This number is generally between 640x480 (640 pixels long, 480 pixels wide) and 1600x1200, but higher resolutions are technically possible.

•

The size: This is calculated by measuring the diagonal of the screen, and is expressed in inches (an inch is about 2.54 cm). Be careful not to confuse a screen's definition with its size. After all, a screen of a given size can display different definitions, although in general screens which are larger in size have a higher definition.

•

The dot pitch: This represents the distance which separates two phosphors of the same colour. The lower the dot pitch, the better the image quality. A dot pitch equal to or less than 0.25 mm will be comfortable to use, while monitors with a dot pitch equal to or greater than 0.28 mm should be avoided.

•

The resolution: This determines the number of pixels per surface unit (given in linear inches). This is abbreviated DPI, for Dots Per Inch. A resolution of 300 dpi means 300 columns and 300 rows of pixels per square inch, which means that there are 90,000 pixels per square inch. By comparison, a resolution of 72 dpi means that one pixel is 1"/72 (one inch divided by 72) or 0.353 mm, which corresponds to one pica (a typographical unit). The terms "resolution" and "definition" are often confused in the media.

•

The refresh rate: This represents the number of images which are displayed per second, or more precisely the number of times the image is refreshed each second. Also called the vertical scan rate, it is expressed in Hertz. The higher this value is, the better the visual comfort (the image does not appear to flicker), so it must be much higher than 67 Hz (any lower than that, and the image appears to "blink"). Most people do not notice the flicker effect at 70 Hz or higher, so a value equal to or greater than 75 Hz is generally suitable.

Flat monitor

NextHard Drive disc

Flat-screen monitors Flat-screen monitors (also called FPDs for Flat panel displays) are becoming more and more widespread, as they take up less space and are less heavy than traditional CRT monitors. What's more, the technology used by flat-screen monitors uses less energy (lower than 10W, as opposed to 100W for CRT monitors) and emits less electromagnetic radiation. Liquid crystal displays

LCD (Liquid Crystal Display) is based on a screen made up of two grooved transparent parallel plates, oriented at 90° to one another; the space between them holds a thin layer of liquid containing certain molecules (liquid crystals) which change direction when they are exposed to electrical current. Combined with a source of light, the first plate acts as a polarizing filter, letting through only those light components whose oscillation is parallel to the grooves.

In the absence of electrical current, the light is blocked by the second plate, which acts as a perpendicular polarising filter.

When powered, the crystals align one by one in the direction of the electric field, and can cross the second plate. By locally controlling the orientation of the crystals, it is possible to make pixels. There are normally said to be two types of flat screens, depending on which control system is used to polarise the crystals: •

"Passive matrix" displays, whose pixels are controlled by row and column. Pixels are given a row/column address using transparent conductors located in the monitor's frame. The pixel lights up when it is addressed, and turns off in when refreshed.

Passive matrix monitors usually use TN technology (Twisted Nematics). Passive matrix monitors often suffer from a lack of brightness and contrast. •

"Active matrix" displays, in which each pixel is controlled individually.

The most common technology for this kind of display is TFT (Thin Film Transistor), which can control every pixel using three transistors (which correspond to the 3 RGB colours). Under this system, the transistor coupled with each pixel can memorise its state, and keep it lit between refreshes. Active matrix monitors are brighter and display a sharper image.

Whether the monitors are active or passive, they need a light source to function. The following terms define how the screen is lit: •

Reflection screens are light from the front, using artificial light or simply ambient light (as with most digital watches).

•

Transmission screens use rear lighting to display information. This type of screen is especially well-suited for indoor use, or in dim light conditions, and normally provides a high-contrast, bright image. On the other hand, they become hard to read when used outdoors (in full sunlight)

•

Transflective screens use rear lighting as well as a polariser made of a translucent material, which can transmit background light while reflecting some ambient light. This type of screen is especially suitable for devices that are meant to be used both indoors and outdoors (such as digital cameras and PDAs).

Plasma screens Plasma technology (PDP, Plasma Display Panel) is based on emitting light by exciting gases. The gas used in plasma screens is a mixture of argon (90%) and xenon (10%). Gas is contained within cells, each one corresponding to a pixel that corresponds to a row electrode and column electrode, which excite the gas within the cell. By modulating the voltage applied by the electrodes and the frequency of excitation, up 256 luminous values can be defined. The gas excited this way produces ultraviolet radiation (which is invisible to the human eye). With blue, green, and red phosphors distributed among the cells, the ultraviolet radiation is converted into visible light, so that pixels (made up of 3 cells) can be displayed in up to 16 million colours (256 x 256 x 256). Plasma technology can be used to create large-scale high-contrast screens, but plasma screens are still expensive. What's more, power consumption is more than 30 times higher than for an LCD screen Specifications The most common specifications for monitors are: •

The definition: The number of pixels that the screen can display. This number is generally between 640x480 (640 pixels long, 480 pixels wide) and 1600x1200, but higher resolutions are technically possible.

•

The size: This is calculated by measuring the diagonal of the screen, and is expressed in inches (an inch is about 2.54 cm). Be careful not to confuse a screen's definition with its size. After all, a screen of a given size can display different definitions, although in general screens which are larger in size have a higher definition.

•

The resolution: This determines the number of pixels per surface unit (given in linear inches). This is abbreviated DPI, for Dots Per Inch. A resolution of 300 dpi means 300 columns and 300 rows of pixels per square inch, which means that there are 90,000 pixels per square inch. By comparison, a

resolution of 72 dpi means that one pixel is 1"/72 (one inch divided by 72) or 0.353 mm, which corresponds to one pica (a typographical unit). •

Response time: Defined by international standard ISO 13406-2, this corresponds to the amount of time needed to switch a pixel from white to black and back again. Response time (expressed in milliseconds) should be as low as possible (pragmatically, lower than 25 ms).

•

Luminance: Expressed in candelas per square metre (Cd/m2), this is used to define the screen's "brightness" The order of magnitude for luminance is about 250 cd/m2.

•

The horizontal and vertical viewing angle: Expressed in degrees, this is used to define the angle from which viewing the screen becomes difficult when the user is not looking at it straight-on.

Hard drive

NextCD-ROM player

The role of the hard drive The hard drive is the component which is used to permanently store data, as opposed to RAM, which is erased whenever the computer is restarted, which is why the term mass storage device is sometimes used to refer to hard drives. The hard drive is connected to the motherboard using a hard drive controller which acts as an interface between the processor and the hard drive. The hard drive controller manages the drives linked to it, interprets commands sent by the processor and routes them to the drive in question. Hard drives are generally grouped by interface as follows: •

IDE

•

SCSI

•

Serial ATA

When the USB standard appeared, external cases which could connect a hard drive using a USB port were released, making hard drives easy to install and increasing storage capacity for macking backups. These are called external hard drives, as opposed to internal hard drives which are plugged directly into the motherboard; still, they are the same disks, even though they are connected to the computer using a case plugged into a USB port. Structure A hard drive is made up of not just one, but several rigid metal, glass, or ceramic disks, stacked very close to one another and called platters.

The disks turn very quickly around an axle (currently several thousand revolutions per minute) in a counter-clockwise direction. A computer works in binart mode, meaning that the data is stored in the form of 0s and 1s (called bits). Hard drives hold millions of these bits, stored very close to one another on a fine magntic layer a few microns thick, which is covered by a protective film. They are read and written using read heads located on both sides of the platters. These heads are electromagnets which raise and lower themselves in order to read or write data. The read heads are only a few microns from the surface, separated by a layer of air created by the rotation of the disks, which generates a wind of about 250km/h (150 mph)! What's more, these disks are laterally mobile, so that the heads can sweep across their entire surface.

However, the heads are linked to one another and only one of them can read or write at a given moment. The term cylinder is used to refer to all the data stored vertically on each of the disks. This entire precision mechanism is contained within a fully airtight case, as the smallest particle can degrade the disk's surface. This is why hard drives are closed shut with seals, and the warning "Warranty void if removed", as only hard drive manufacturers can open them (in particle-free "cleanrooms"). How it works The read/write heads are said to be "inductive", meaning that they can generate a magnetic field. This is especially important in writing: The heads, by creating positive or negative fields, polarise the disk surface in a very tiny area, so that when they are read afterwards, the polarity reversal completes a circuit with the read head, which is then transformed by an analog-digital converter (ADC) into a 0 or 1 which can be understood by the computer.

The heads start writing data from the edge of the disk (track 0), then move onward towards the centre. The data is organised in concentric circles called "tracks", which are created by low-level formatting. The tracks are separated into areas (between two radii) called sectors, containing data (generally at least 512 octets per sector).

The term cylinder refers to all data found on the same track of different platters (i.e. above and below one another), as this forms a "cylinder" of data.

Finally, the term clusters (also called allocation units) refers to minimum area that a file can take up on the hard drive. An operating system uses blocks, which are in fact groups of sectors (between 1 and 16 sectors). A small file may occupy multiple sectors (a cluster). On old hard drives, addressing was done physically, by defining the position of the date from the coordinates Cylinder/Head/Sector (CHS). Block mode

Block mode and 32-bit transfer are used to get the best performance out of your hard drive. Block mode involves transferring data in blocks, usually in 512-byte packets, which keeps the processor from having to process a large number of tiny one-bit packets. This way, the processor has the "time" to perform other operations. Unfortunately, this data transfer mode is only useful for older operating systems (such as MS-DOS), as recent operating systems use their own hard drive manager, which makes this management system obsolete. There is a BIOS option (IDE HDD block mode or Multi Sector Transfer) which can sometimes determine how many blocks can be managed at once. It is a number between 2 and 32. If you don't know it, there are several solutions available: •

Check your hard drive's documentation

•

Search for the drive's specifications on the Internet

•

Carry out tests to determine it.

Still, block mode may generate errors in certain systems, due to redundancies in the hard drive manager. The system involves disabling one of the two managers: •

the 32-bit software manager in the operating system;

•

block mode in the BIOS.

32-bit mode 32-bit mode (as opposed to 16-bit mode) is characterised by 32-bit data transfers. 32-bit transfer is comparable to 32 doors opening and closing all at once. In 32-bit mode, two 16-bit words (groups of bits) are transmitted one after another, then assembled. The improvements in performance when switching from 16-bit mode to 32-bit mode are generally insignificant. In any event, it is no longer normally possible to select the mode, as the motherboard automatically determines which mode to use depending on the type of hard drive. However, automatically selecting 32-bit mode may slow down IDE CD-ROM drives whose speed is higher than 24x when they are alone on an IDE ribbon cable. Indeed, when a CD-ROM drive is alone on the cable, the BIOS cannot tell if it is compatible with 32-bit mode (because it is looking for a hard drive), in which case it switches to 16-bit mode. In this case, the transfer speed (incorrectly called the transfer rate) will be lower than the one claimed by the manufacturer. The solution is to plug the CD-ROM drive and a 32-bit-compatible hard drive into the same ribbon cable. Technical specifications •

Capacity: Amount of data which can be stored on a hard drive.

•

Transfer rate: Quantity of data which can be read or written from the disk per unit of time. It is expressed in bits per second.

•

Rotational speed: The speed at which the platters turn, expressed in rotations per minute (rpm for short). Hard drive speeds are on the order of 7200 to 15000 rpm. The faster a drive rotates, the higher its transfer rate. On the other hand, a hard drive which rotates quickly tends to be louder and heats up more easily.

•

Latency (also called rotational delay): The length of time that passes between the moment when the disk finds the track and the moment it finds the data.

•

Average access time: Average amount of time it takes the read head to find the right track and access the data. In other words, it represents the average length of time it takes the disk to provide data after having received the order to do so. It must be as short as possible.

•

Radial density: number of tracks per inch (tpi).

•

Linear density: number of bits per inch (bpi) on a given track.

•

Surface density: ratio between the linear density and radial density (expressed in bits per square inch).

•

Cache memory (or buffer memory): Amound of memory located on the hard drive. Cache memory is used to store the drive's most frequently-accessed data, in order to improve overall performance;

•

Interface: This refers to the connections used by the hard drive. The main hard drive interfaces are: o

IDE/ATA

o

Serial ATA

o

SCSI

o

However, there are external cases used for connecting hard drives with USB or FireWire ports.

CD, CD audio and CD-ROM

NextDVD-ROM player

The Compact Disc was invented by Sony and Philips in 1981 in order to serve as a high-quality compact audio storage device which allowed for direct access to digital sound tracks. It was officially launched in October 1982. In 1984, the Compact Disc's specifications were extended (with the publication of the Yellow Book) so that it could store digital data. CD geometry A CD (Compact Disc) is an optical disc 12cm in diameter and 1.2mm thick (its thickness may vary from 1.1 to 1.5 mm) for storing digital information: up to 650 MB of computer data (equivalent to 300,000 typed pages) or 74 minutes of audio data. A circular hole 15mm in diameter is used to centre it on the CD player's surface. The makeup of a CD A CD is built from a plastic (polycarbonate) substrate and a fine, reflective metallic film (24-carat gold or a silver alloy). The reflective layer is then covered with an antiUV acrylic finish, creating a protective surface for data. Finally, an additional layer may be added so that data can be written on the other side of the CD as well.

The reflective layer contains tiny bumps. When the laser passes over the polycarbonate substrate, light is reflected off the reflective surface, but when the laser reaches a bump, that's what allows it to encode information. This information is stored in 22188 tracks engraved in grooves (though it's actually just one track spiralling inward).

Commercially purchased CDs have already been pressed, meaning that the bumps have been created used plastic injected into a mold which contains the desired pattern in reverse. A metallic layer is then affixed onto the polycarbonate substrate, and this layer is itself covered with a protective coating. Blank CDs (CD-R), by contrast, have an additional layer (located between the substrate and metallic layer) made of a dye which can be marked (or "burned") by a high-powered laser (10 times as powerful as the one used for reading them). It is the dye layer which either absorbs or reflects the beam of light emitted by the laser.

The most commonly used dyes are: •

Blue-coloured cyanine, which appears green when the metallic layer is made of gold

•

Light-green-coloured pthalocyanine, which appears gold-coloured when the metallic layer is made of gold

•

Dark-blue-coloured azo

As the information is not stored as pits but as coloured marks, a pre-groove is placed in the blank disc to help the burner follow the spiral path, so that precision engineering is not needed on CD burners. What's more, this pre-groove follows a sine wave called a wobble, with an amplitude of +/-0.03µm (30nm) and a frequency of 22.05kHz. The wobble lets the burner know what speed it needs to record at. This information is called ATIP (Absolute Time in Pre-Groove).

Operation The read head is made of a laser (Light Amplification by Stimulated Emission of Radiation) which emits a beam of light, and a photoelectric cell which captures the reflected beam. CD players use an infrared laser (with a wavelength of 780 nm), as it is compact and inexpensive. A lens located near the CD focuses the laser beam onto the pits. A semi-reflective mirror allows the reflected light to strike the photoelectric cell, as shown in the following diagram:

A "pickup" moves the mirror so that the read head can access the entire CD-ROM. A CD has two basic operating modes: •

Reading at a constant linear velocity (or CLV for short). This was the operating mode of the earliest CD-ROM drives, based on how CD audio players and even old turntables work. When a disc turns, the grooves closer to the centre run more slowly than the grooves on the outer edge, so the read speed (and therefore the speed at which the disc rotates) has to adjust based on the radial position of the read head. With this process, the information density is the same throughout the disc, so there is an increase in capacity. CD audio players have a linear velocity between 1.2 and 1.4 m/s.

•

Reading at a constant angular velocity (CAV) involves adjusting the information density depending on where the data is located, so that the rotation speed is the same at every point on the disc. This means that data density will be lower on the edge of the disc and higher near the centre.

A CD-ROM drive's reading velocity originally corresponded to the speed of an audio CD player, a rate of 150 kB/s. This speed was then adopted as a reference point and termed 1x. Later generations of CD-ROM drives have been described using multiples of this value. The following table shows the read speed for each multiple of 1x: Read speed Response time 1x 150 kB/s

400 to 600 ms

2x 300 kB/s

200 to 400 ms

3x 450 kB/s

180 to 240 ms

4x 600 kB/s

150 to 220 ms

6x 900 kB/s

140 to 200 ms

8x 1200 kB/s

120 to 180 ms

10 1500 kB/s x

100 to 160 ms

12 1800 kB/s x

90 to 150 ms

16 2400 kB/s x

80 to 120 ms

20 3000 kB/s x

75 to 100 ms

24 3600 kB/s x

70 to 90 ms

32 4500 kB/s x

70 to 90 ms

40 6000 kB/s x

60 to 80 ms

52 7800 kB/s x

60 to 80 ms

Encoding information The physical track is made up of bumps 0.168µm deep and 0.67µm wide, with variable length. The "rings" in the spiral are spread about 1.6µm apart from one another. Pits are the term for the depressions in the groove, and lands are the spaces between them.

The laser used for reading CDs has a wavelength of 780 nm when travelling through air. As the polycarbonate's refractive index is 1.55, the laser's wavelength in the polycarbonate is equal to 780/1.55 = 503nm = 0.5µm. Since the depth of the groove is one quarter the wavelength of the laser beam, a light wave reflected by a pit travels half again as long (125% as long to hit the disk and the same to return) as a wave reflects by a land. This way, whenever the laser strikes a pitted groove, the wave and its reflection are dephased by a half wavelength and cancel one another out (destructive interference), so it's as if no light was reflected at all. Moving from a pit to a land causes a drop in the signal, which represents one bit. The length of the groove is what stores the information. The size of a bit on a CD ("S") is standardised and corresponds to the distance travelled by the light beam in 231.4 nanoseconds, or 0.278µm and the standard minimum velocity of 1.2 m/s. In the EFM standard (Eight-to-Fourteen Modulation), used for storing information on a CD, there must always be at least two bits set to 0 between two consecutive 1 bits, and there cannot be more than 10 consecutive zero bits between two 1 bits, in order to avoid errors. This is why the length of a groove (or a land) is greater than or equal to the length needed to store the value OO1 (3S, or 0.833µm) and less than or equal to the length of the value 00000000001 (11S, or 3.054µm).

Standards There are numerous standards describing the ways in which information must be stored on a compact disc, depending on how it is to be used. These standards are set out in documents called books, each of which has a colour assigned to it: •

Red book (also called RedBook audio): Developed in 1980 by Sony and Philips, it describes the physical format of a CD and the encoding method for

an audio CD (sometimes called CD-DA for Compact Disc - Digital Audio). It defines a sample rate of 44.1 kHz and 16-bit resolution (in stereo) for recording audio data. •

Yellow book: Developed in 1984 in order to describe the physical format for data CDs (CD-ROM for Compact Disc - Read Only Memory). It includes two modes: o

CD-ROM Mode 1, used for storing data with error-correction (called ECC, for Error Correction Code) in order to avoid losing data due to degradation of the disc.

o

CD-ROM Mode 2, used for storing compressed graphical, video, and audio data. To be able to read this type of CD-ROM, a drive must be Mode 2 compatible.

•

Green book: Physical specifications for a CD-I (CD Interactive, by Philips)

•

Orange book: Physical format for writable CDs. It is divided into three sections: o

Part I: The CD-MO format (magneto-optical disks)

o

Part II: The CD-WO format (Write Once, now called CD-R)

o

Part III: The CD-RW format (CD Rewritable)

•

White book: Physical format for video CDS (VCD)

•

Blue book: Physical format for "Extra" CDs (CD-XA)

Logical structure The Orange Book dictates that a CD-R, whether it is an audio CD or a CD-ROM, is made up of three areas which form the information area: •

The Lead-in Area (sometimes called the LIA) only contains information which describes the contents of the disc (in the TOC, Table of Contents). The Lead-in Area extends from a radius of 23 mm from the edge to a radius of 25 mm. This size is required by the need to be able to store information about a maximum of 99 tracks. The Lead-in Area lets the CD player/drive follow the spiralling pits in order to synchronise itself with the data found in the program area.

•

The Program Area is the section of the disc which contains the data. It starts 25 mm out from the centre, extends to a radius of 58mm, and can contain the equivalent of 76 minutes of audio data. The program area can contain up to 99 tracks (or sessions), each at least 4 seconds long.

•

The Lead-Out Area (or LOA), containing null data (silence on an audio CD) marks the end of the CD. It starts at a radius of 58 mm and must be at least 0.5 mm in width (radially). The Lead-Out Area must contain at least 6750 sectors, or 90 seconds of silence at minimum speed (1X).

Besides the three areas described above, a CD-R contains a PCA (Power Calibration Area) and a PMA (Program Memory Area), which together form the SUA (System User Area). The PCA can be seen as a testing area for the laser, so that it can calibrate its power depending on the kind of disk being read. This area is what makes it possible to sell blank CDs that use different dyes and reflective layers. Each time it is readjusted, the burner notes that it has carried out a test. Up to 99 tests are allowed per disc. File systems The format of the CD (or more precisely, the file system) describes how the data is stored in the program area. The earliest file system for CDs was the High Sierra Standard. The ISO 9660 format, standardised in 1984 by the ISO (International Standards Organization) revisited the High Sierra Standard in order to define the structure of files and folders on CD-ROMs. It is divided into three levels: •

Level 1: An ISO 9660 Level 1-formated CD-ROM may only contain files with names made up entirely of capital letters (A-Z), digits (0-9) and the character "_". Together, these are called d-characters. Folder names are limited to 8 dcharacters and can be no more than 8 subfolders deep. Additionally, the ISO 9660 standard requires each file to be stored continuously on a CD-ROM, without fragmentation. It is the most restrictive level. Compliance with Level 1 ensures that the disc will be readable on large number of platforms.

•

Level 2: The format ISO 9660 Level 2 requires that each file be stored as a continuous flow of bytes, but is more flexible with file names, allowing the characters @ - ^ ! $ % & ( ) # ~ and up to 32 subfolders deep.

•

Level 3: The format ISO 9660 Level 3 does not restrict file names or folders.

Microsoft has also defined the Joliet format, an expansion of ISO 9660 which allows long file names (LFNs) of up to 64 characters, including spaces and accented characters (based on Unicode). The ISO 9660 Romeo format is a naming option offered by Adaptec, independent of Joliet, for storing files whose names can be as long as 128 characters, but which does not support Unicode encoding. The ISO 9660 RockRidge format is a naming extension to ISO 9660 which makes it compatible with UNIX file systems. In order to make up for the limitations of ISO 9660 (which make it unsuitable for DVD-ROM discs), the OSTA (Optical Storage Technology Association) has developed the ISO 13346 format, known under the name UDF (Universal Disk Format). Writing methods •

Monosession: This method creates a single session on the disc and does not allow new data to be added later.

•

Multisession: Unlike the previous method, this one lets a CD be written to several times, by creating a 14MB-long table of contents (TOC) de 14Mo for each session.

•

Multivolume: This is multisession recording which considers each session as a separate volume.

•

Track At Once: This method is used for disabling the laser between two tracks, in order to create a two-second pause between each track on an audio CD.

•

Disc At Once: Unlike the previous method, Disc At Once writes a whole CD all at once (without pausing).

•

Packet Writing: This methods lets data be recorded in packets.

Technical specifications A CD-ROM drive is defined by the following: •

Speed: The speed is calculated relative to the speed of an audio CD player (150 KB/s). A drive which can reach speeds of 3000KB/s would be called 20X (20 times faster than a 1X drive).

•

Access time: This represents the average time it takes to go from one part of the CD to another.

•

Interface: ATAPI (IDE) or SCSI;

DVD, DVD audio and DVD-ROM (DVD-R, DVD-RW, DVD+W, DVD+RW)NextUSB key

Introduction to the DVD format The DVD (Digital Versatile Disc, or less commonly Digital Video Disc) is an "alternative" to the compact disc (CD) with six times as much storage space (for the lowest-capacity kind of DVD — single-layer, single-sided). The DVD format was designed to provide a universal storage medium, while the CD was originally designed as an audio medium only.

The DVD is designed to make data addressable and accessible at random (nonsequentially). It has a complex structure which provides greater interactivity, but requires more advanced microprocessors The DVD format was originally supported (starting 15 September 1995) by a consortium of ten multimedia companies (Hitachi, JVC, Matsushita, Mitsubishi, Philips, Pioneer, Sony, Thomson, Time Warner and Toshiba). Starting in 1997, a new consortium called "DVD Forum", succeeded the initial one. A DVD can easily be confused with a CD, as both are plastic discs 12 cm in diameter and 1.2 mm thick, which are read using a laser beam. However, CDs use an infrared laser with a wavelength of 780 nanometres (nm), while DVD burners use a red laser with a wavelength of 635 nm or 650 nm. What's more, CD players generally use a lens with a focus of 0.5, while the lenses of DVD players have a focus of 0.6. For this reason, DVDs have grooves whose minimum height is 0.4µ with a pitch of 0.74µ, as opposed to 0.834µ and 1.6µ for a CD.

The main reason to use DVDs is their storage capacity, which makes them an excellent medium for video. A 4.7GB DVD can store more than two hours of compressed video in MPEG-2 (Motion Picture Experts Group), a format used for compressing images while still keeping them high-quality. Physical structure DVDs exist in both "single layer" and "dual layer" (DL) versions. Dual layer discs are made up of a translucent, gold-based semi-reflective layer and an opaque, silverbased reflective layer, separated by a bonding layer. In order to read both these layers, the drive has a layer which can change its intensity by modifying its frequency and focus: •

with low intensity the beam is reflected off the outer gold surface;

•

with higher intensity, the beam passes through the first layer is reflected off the inner silver surface.

The inner layer, however, has a lower density. Additionally, it stores the information "upside down" on an inverted spiral, in order to limit latency when moving from one layer to the other.

What's more, DVDs exist both in single-sided and double-sided versions, like vinyl records. In the latter case, the information is stored on both sides of the disc. DVD discs are generally divided into four families, each with different storage capacities depending on their physical characteristics: Type of disc

Characteristics

CD

Storage capacity

Equivalent in music (hours:minutes)

Equivalent in number of CDs

650MB

1:14

1

4.7 GB

9:30

7

DVD-5

single-sided, single layer

DVD-9

single-sided, dual layer8.5 GB

17:30

13

DVD-10

double-sided, single layer

9.4 GB

19:00

14

DVD-17

double-sided, dual layer

18 GB

35:00

26

Standard DVD formats The official specifications for DVD are divided into five books: •

Book A for DVD-ROM;

•

Book B for DVD Video;

•

Book C for DVD Audio;

•

Book D for writeable (DVD-R) and rewritable (DVD-RW) DVDs. The DVD-R format is Write-Once, while DVD-RW is a rewritable format, which lets data be rewritten using a phase-change metallic alloy;

•

Book E for rewritable DVDs (also called DVD-RAM, for DVD Random Access Memory). DVD-RAM is a rewritable medium which uses phase-change technology to record data. DVD-RAMs are actually cartridges which are composed of a case and a DVD. Some cartridges are removable, so that a DVD-RAM can be played in a DVD player.

Standard DVD recording formats There are currently three recordable DVD formats: •

DVD-RAM by Toshiba © and Matsushita ©. This format is mainly used in Japan.

•

DVD-R/DVD-RW, supported by the DVD Forum. DVDs in DVD-R format can only be recorded once, while DVD-RWs can be rewritten up to about 1000 times. The DVD-R format, as well as DVD-RW, can store up to 4.7 GB on a disc.

•

DVD+R / DVD+RW, supported by Sony and Philips within the DVD+RW Alliance, which also includes Dell, Hewlett-Packard, Mitsubishi/Verbatim, Ricoh, Thomson and Yamaha.

These three formats are incompatible with one another, despite their similar performance. The DVD-RAM format will not be discussed at length here, as it is mainly used in Japan. The DVD-R(W) and DVD+R(W) formats, on the other hand, are widely used in Europe and North America. DVD-R/RW The DVD-R/DVD-RW format is based on what is known as "pre-pit" technology. As with CD-Rs, writeable and rewriteable DVDs use a "pre-groove" (a spiral groove already engraved on the disc), which follows a sine wave called a wobble. The pregroove defines the position for the record head to be placed on the disc (called tracking) while the oscillating frequency lets the burner adjust its speed. Address information (i.e. where the data is located), by contrast, is defined using recesses pre-engraved onto the disc in the pits between the disc's groove, called "land prepits" (or LPP for short).

Pre-pits form a second signal, which used for positioning data. When the laser reaches a pre-pit, an amplitude peak appears in the oscillation, which lets the burner know that data must be recorded The DVD-R specifications make it clear that a prepit must be at least one period long (1T). The DVD-R/DVD-RW format offers error handling features, which are mainly software-based (called Persistent-DM and DRT-DM). DVD+R/RW The DVD+R/DVD+RW format uses a groove whose oscillation (wobble) has a much higher frequency than DVD-Rs (817.4 kHz for DVD+R versus 140.6 for DVD-R) and handles addresses by phase-modulating the wobble, a kind of phase-inversion encoding called ADIP (ADdress In Pre-groove). This phase inversion takes place every 32 periods (32T).

The DVD+RW format has an error-correction feature called DVD+MRW (Mount Rainier for DVD+RW) used to mark defective blocks. What's more, if readable data is found on that block, there is a mechanism for moving them to a healthy block and updating the file allocation table (this process is called Logical to Physical Address Translation). What's more, the specifications provide for a check to run in the background, in order to check errors found on the disc while the reader is inactive. The user can still read the disc or eject it at any time; if this happens, the error check will continue where it left off as soon as the player is idle again. Difference between DVD+ and DVDGenerally speaking, the address method used by DVD+R (phase modulation) has a higher resistance to electromagnetic disturbances than the pre-pit method. When writing a disc, the write head must also read the pre-pits in order to position the data in the right place. Thus, the light emitted by the laser may cause disturbances.

What's more, given the period which corresponds to the length of a pre-pit (T1), the pre-pits are much harder to detect when the disc is being read more quickly. So it's not surprising that the first 16x burner on the market was DVD+RW. This is why the DVD+R(W) format, for more recent technological specifications, offers better performance as well as additional features. On the other hand, DVDR(W) has been ratified by the DVD Forum and was the first format used, so the majority of DVD drives (and especially DVD players) are compatible with it. Most DVD burners support both formats. In conclusion, given that it is more compatible with standalone DVD players, DVD-R(W) is preferred for creating Video DVDs, while DVD+R(W) is superior for creating data discs. DVD DL The term "DVD DL" (DVD Dual Layer) refers to DVDs which can be recorded on two separate layers. These discs, which have more storage space than single-layer DVDs, use a technology similar to that of DVD-9 (dual-layer discs). Logical structure A DVD is essentially made up of three zones, which represent the information area: •

The Lead-in Area (or LIA for short) only contains data which describes the disc's contents (this information is stored in the Table of Contents, or TOC). The Lead-in Area lets the DVD player/drive follow the spiralling pits in order to synchronise itself with the data found in the program area.

•

The Program Area is the area which contains the data.

•

The Lead-Out Area (or LOA for short), containing null data (silence on an audio DVD) marks the end of the DVD.

Besides the three areas described above, a recordable DVD contains a PCA (Power Calibration Area) and an RMA (Recording Management Area) located before the Lead-In Area.

The PCA can be seen as a testing area for the laser, so that it can calibrate its power depending on the kind of disc being read. This area is what makes it possible to sell blank CDs that use different dyes and reflective layers. Each time it is readjusted, the burner notes that it has carried out a test. Up to 99 tests are allowed per disc. File and folder system DVDs use the file system UDF (Universal Disk Format). In order to remain somewhat compatible with older operating systems, a hybrid file system called "UDF Bridge", which supports both UDF and the ISO 9660 file system used by CD-ROMs, has been created. Nonetheless, it is important to note that DVD video and audio players do not support UDF. Structure of a video DVD A video DVD may contain data for standalone DVD players, as well as additional data that can be read by a computer. A video DVD has a hierarchical folder organisation for storing video and audio data. It normally relies on the following structure:

The main directory, named VIDEO_TS (for Video Title Sets), holds the DVD video files. The AUDIO_TS directory is for DVD audio, but it is sometimes required by certain DVD players. JACKET_P contains images of the DVD's cover art. Lastly, you can also add other folders to it, which can be read by a computer. A video DVD is made up of a certain number of elements found in the VIDEO_TS directory: •

A video manager (VMG). The VMG generally includes the introductory video clip, as well as the menu which gives access to the other video titles (including the submenus).

•

One or more video titles sets (VTS), containing video titles.

The "video titles" may be films, videos or albums. A title is made up of "Video Object Block Sets" (VOBS), each containing: •

a "control file" (called VTSI, for Video Title Set Information), and containing navigation data.

•

one or several video objects (VOB, Video Object Block). The video object (VOB) is the basic element of the DVD. It contains video and audio data and multiplexed images, all in MPEG2 format. A .VOB file may be read by a software video player by changing its extension to ".MPG". The DVD format's specifications require all VOB files to be no larger than one gigabyte. Each

VOB is made up of "cells", which represent the various video or audio clips that make up the VOB, such as video chapters or the songs on an album. •

a copy of the VTSI (VTSI Backup).

A DVD can contain up to 99 titles (VTS), each divided into up to 10 chapters. The VIDEO_TS directory usually contains three types of files with the following extensions: •

IFO, containing navigation data (it corresponds to the Video Manager).

•

VOB (Video Object Block), containing video streams, the audio channels and the subtitles for a video title.

•

BUP (BUP stands for Backup), which contains a backup of the IFO files, in case they become unreadable.

The special file named VIDEO_TS.IFO (IFO stands for information) contains the information needed for the DVD player to display the main menu. It is accompanied by the fileVIDEO_TS.VOB, which contains the opening animation, as well as a backup file (named VIDEO_TS.BUP). Regions Video DVDs are designed to only be readable in certain parts of the world, which has been divided into regions (originally meant to limit the distribution of bootlegs). Theoretically, it is impossible to play a DVD from one region on a player from a different one. However, nearly all computer DVD drives and many standalone players can be made "region-free" using special tools.

USB Key

NextKeyboard

Introduction to USB keys A USB key is a compact-format removable storage device which can be plugged into a computer's USB port. A USB key is a plastic shell carrying a USB connector and flash memory, a solidstate, non-volatile, rewritable kind of memory; that is, it has many of the same characteristics as RAM, except that the data is not wiped out when the machine is turned off. For this reason, a USB key can store up to several gigabytes of data, and keep the data saved when electrical power is cut off (i.e. when the key is unplugged). In practice, a USB key is very practical for users who go from one computer to another, as it is very easy to transport and can store a large quantity of documents and data. What's more, recent motherboards can boot from USB keys, which means that you can now start an operating system from a simple USB key! Very useful for users who want to carry their own work environment wherever they go, or for restarting and fixing a system after a crash. Characteristics The features to take into account when choosing a USB key are: •

Storage capacity

•

Transfer rate: This is the speed at which data is transfered. It should be noted that the transfer rate when reading is different from the transfer rate when writing, as the process of writing to flash memory is slower. The transfer rate depends on the read speed and write speed of the Flash memory component, as well as the USB standard supported: o

USB 1.1 (low-speed USB), which can reach 12 Mbit/s,

o

USB 2.0 (high-speed USB) which can reach 480 Mbit/s. It should be noted that in order to attain the full transfer speed, the key must be plugged into a USB 2.0 port. Otherwise (with a USB 1.1 port), the key will run at a low speed.

•

Encryption features: Some keys have tools for encrypting data or some of the data found on the key, in order to strengthen privacy.

•

Write protection: Some keys include a hardware switch for putting the key in read-only mode, to prevent data from being changed or erased.

•

Multimedia functions: When a USB key includes a headphone jack and can play audio files (generally in the MP3 format), it is called an MP3 player.

The keyboard

NextMouse

Introduction to the keyboard The keyboard, like a typewriter, is used for entering characters (such as letters, numbers, and symbols). It is an essential input device for a computer, as it is what lets us enter commands. The term "QWERTY" (after the first six letter keys on the keyboard) refers to the type of keyboard which is used with nearly all computers in the English-speaking world. In other countries, keyboard layouts are different. The Qwerty keyboard was designed in 1868 in Milwaukee by Christopher Latham Sholes, who placed the keys corresponding to the most commonly used letter pairs at opposite ends of the keyboard, in order to prevent the typewriter hammers of the time from becoming jammed with one another. This keyboard was first sold by the company Remington in 1873. Therefore, the Qwerty keyboard was designed from a purely technical perspective, hindering usability and efficiency. Legend has it that the placement of keys along the first row of the Qwerty keyboard was motivated by typewriter dealers of the time, who wanted all the keys needed to type the word "typewriter" to be conveniently located when demonstrating the product. In 1936, August Dvorak (a professor at the University of Washington) created a keyboard whose keys were arranged solely with efficiency in mind. The Dvorak keyboard placed all the vowels of the alphabet and the five most common consonants on the central row so they could be easily accessed, while also evenly dividing the work between the left and right hands. What's more, the most frequent letters of the alphabet were placed at the centre of the keyboard.

Various studies showed that the increased efficiency of the Dvorak keyboard was small in practice and that the amount of effort required to switch from the Qwerty keyboard to Dvorak's was too much to be worth the trouble, which explains why all computers today still have Qwerty keyboards. Keyboard connector Keyboards are generally plugged into the rear of the CPU, on the motherboard, using a purple PS/2 connector:

How it works

Whenever a key is pressed, a specific signal is transmitted to the computer. The keyboard uses a crossbar network to identify every key based on its row and column

When a key is pressed, an electrical contact is formed between the row and column. The electric signals are transmitted to a microcontroller, which sends a code (BCD, ASCII or Unicode) to the computer describing the character which corresponds to that key. Types of keyboards There are four types of keyboards for PCs. The first three were invented by IBM, while the latter is the result of changes made when Microsoft Windows 95 was released. These are the four kinds of keyboards: •

The 83-key keyboard (PC/XT)

•

The 84-key keyboard (PC/AT)

•

The 102-key keyboard, called the extended keyboard

•

The 105-key Microsoft Windows 95-compatible keyboard.

PC/XT keyboards This was the first keyboard for the PC, and was unusual in that it was separate from the computer, unlike the other computers of the time (such as the Apple II and the Amiga), whose keyboards were integrated within them.

This keyboard included 83 keys, but was criticised for the arrangement of the keys and their disproportionate size (especially the Shift and Enter keys, which were too small and poorly placed). What's more, communication between the keyboard and the CPU was one-way, meaning that the keyboard couldn't include an LED indicator. PC/AT keyboards The PC/AT keyboard, which had 84 keys, was introduced for the PC/AT computer in 1984.

This keyboard corrected the errors of its predecessor, largely by resizing the Shift and Enter keys. Additionally, the keyboard was bidirectional, meaning that it could display its status using LED indicator lights. Finally, the motherboard on the PC/AT included a controller for adjusting the settings: •

The repetition frequency (the number of characters sent per second when a key was depressed)

•

The repetition delay: The length of time before a computer would consider a key to be depressed, in order to distinguish typing a single character from holding down a key

Extended keyboards The new IBM-compatible computers launched in 1986 came with 102-key keyboards.

This new keyboard included different blocks of keys: Starting with this model, the function keys were moved to the top of the keyboard, while cursor control keys, represented by arrows, were added. Microsoft Windows-compatible keyboards Microsoft has defined three new keys, which are used for shortcuts to certain Windows features.

These three new keys are, from left to right: •

The left Windows key

•

The right Windows key

•

The Application key

Here are a few shortcuts using these new keys: Combination Description WIN - E

Display the browser

WIN - F

Find a file

WIN - F1

Show help

WIN - M

Minimise all desktop windows

WIN - Pause Show system properties WIN - Tab

Scroll through the taskbar

WIN - R

Show the "Run" dialog box

The mouse

NextPrinter

Introduction to the mouse The mouse is a pointing device used to move a cursor on the screen and allowing objects to be selected, moved and manipulated using the buttons. The consistent action of pressing (clicking) on a button in order to carry out an action is called a "click". The first mouse was invented and developed by Douglas Carle Engelbart of the Stanford Research Institute (SRI): it was a wooden mouse containing two perpendicular discs and connected to the computer by a pair of twisted wires. Mouse connector The mouse is generally plugged in to the back of the central processing unit, into the motherboard, with a green PS/2 connector:

Some mice, with advanced functionalities sometimes have a USB connector. Types of mice There are several types of mice, classified according to the positioning technology on the one hand and the data transmission to the central processing unit on the other. We can therefore distinguish several large categories of mice: •

Mechanical mice, where the operation is based on a ball (in plastic or rubber) encased in a frame (in plastic) transmitting the movement to two rollers;

•

Optical-mechanical mice, where the operation is similar to that of mechanical mice, except the movement of the ball is detected by optic sensors.

•

Optical mice, capable of determining movement through visual analysis of the surface upon which they slide.

Mechanical mouse The mechanical mouse comprises of a ball upon which two rollers turn. These rollers each comprise of a notched disc which turns between a photodiode and LED (Light Emitting Diode) allowing the light to pass through in sequence. When the light passes through, the photodiode sends a bit (1), when it meets an obstacle, the photodiode sends a zero bit (0). Using this information, the computer knows the position of the cursor and even its speed.

Tip: As you use it, dust settles on the mouse rollers preventing them from turning correctly and causing strange reactions in the cursor. To remedy this, simply open the cage containing the ball and clean the rollers (with a toothbrush for example). Optical mouse The optical mouse operates by analysing the surface on which it moves. So, an optical mouse is comprised of an LED, an image acquisition system (IAS) and a digital signal processor (DSP). The LED is responsible for shining on the surface so as to enable the IAS to get an image of the surface. The DSP, through analysing the microscopic characteristics of the surface determines the horizontal and vertical movement. Optical mice operate on any slightly uneven or even coloured surface. The main advantages of this type of pointing device in comparison to the mechanical mouse are greater precision along with less dirtiness. Cordless mouse Cordless mice are more and more popular because they can be used without physically being connected to the computer, which gives a sensation of freedom. There are also several categories of cordless mice, depending on the technology used: •

Infrared mouse (IR) these mice are used with an infrared receiver connected to the computer. The range of this type of device is a few metres at most with direct line of sight in the same way as a television remote.

•

Hertzian mouse: these mice are used with a hertzian receiver, generally proprietary to the manufacturer. The range of this type of device is around ten metres at most, not necessarily with direct line of sight to the computer. This type of device can be practical for people connecting their computer to their television in another room.

•

Bluetooth mouse: these mice are used with a Bluetooth receiver connected to the computer. The range of this type of device is the same as the propriety hertzian technologies.

Mouse wheel Mice are increasingly equipped with a wheel. The wheel, generally located between the right and left buttons makes it possible to scroll through pages while enabling the user to move the cursor on the screen. The Printer NextScanner

Printers The printer is a peripheral that allows you to make a print-out (on paper) of computer data. There are several printer technologies, the most common of which are: •

the daisy wheel printer

•

the dot-matrix printer (also called impact matrix printer)

•

the inkjet printer and the bubble jet printer

•

the laser printer

Today, daisy wheel printers and matrix printers are hardly ever used. Characteristics The printer is generally characterised by the following elements: •

Print speed: expressed in pages per minute (ppm), print speed represents the printer's ability to print a large number of pages per minute. For colour printers, a distinction is generally made between monochrome and colour print speed.

•

Resolution: expressed in dots per inch (abbreviated as dpi), resolution means the sharpness of printed text. Sometimes the resolution is different for a monochrome, colour or photo print-out.

•

Warm-up time: the waiting time necessary before the first print-out. A printer cannot print when it is "cold". A certain temperature must be reached for the printer to run optimally.

•

Onboard memory: the quantity of memory that allows the printer to store print jobs. The higher the amount of memory, the longer the printer queue can be.

•

Paper format: depending on their size, printers are able to accept different sized documents, generally in A4 format (21 x 29.7 cm) or less frequently A3 (29.7 x 42 cm). Some printers allow you to print on other types of media, such as CDs or DVDs.

•

Paper feed: the method of loading paper into the printer, characterising the way in which blank paper is stored. The paper feed can change depending on where the printer will be placed (rear loading is advised for printers that will be up against a wall).* The main paper feed modes are: o

The feed tray, which uses an internal paper feed source. Its capacity is equal to the maximum number of sheets of paper that the tray can fit.

o

The sheet feeder is a manual feed method that allows you to insert sheets of paper in small quantities (of about 100). The sheet feeder in the back of the printer is either horizontal or vertical.

•

Cartridges: cartridges are rarely standard and depend highly on the printer brand and model. Some manufacturers favour multicoloured cartridges whereas others offer separate ink cartridges. Separate ink cartridges are on the whole cheaper because often one colour is used more than others.

It is interesting to examine the printing cost per sheet. The size of the ink drop is especially important. The smaller the drop of ink, the lower the printing cost will be and the better the image quality will be. Some printers produce drops that are 1 or 2 picolitres. •

Interface: how the printer is connected to the computer. The main interfaces are: o

USB

o

Parallel

o

Network: this type of interface allows several computers to share one printer. There are also WiFi printers that are available through a wireless network

Daisy Wheel Printer Daisy wheel printers are based on typewriters. A matrix in the shape of a daisy contains "petals" that each have one raised character. To print the text, a ribbon of ink is placed between the daisy and the sheet of paper. When the matrix hits the ribbon it leaves ink on paper in the shape of the character on the petal. These printers are obsolete because they are extremely noisy and very slow. Dot-Matrix Printer The dot-matrix printer (sometimes called a matrix printer or an impact printer) allows you to print documents on paper thanks to the "back and forth" motion of a carriage housing a print head. The head is made up of tiny metal pins, driven by electromagnets, which strike a carbon ribbon called an "inked ribbon", located between the head and the paper.

The carbon ribbon scrolls by so that there is always ink on it. At the end of each line, a roller makes the sheet advance.

The most recent dot-matrix printers are equipped with 24-needle printer heads, which allows them to print with a resolution of 216 dpi (dots per inch). Inkjet Printer and Bubble Jet Printer The inkjet printer technology was originally invented by Canon. It is based on the principle that a heated fluid produces bubbles. The researcher who discovered this had accidentally brought a syringe filled with ink into contact with a soldering iron. This created a bubble in the syringe that made the ink in the syringe shoot out. Today's printer heads are made up of several nozzles (up to 256), equivalent to several syringes, which are heated up to between 300 and 400°C several times per second. Each nozzle produces a tiny bubble that ejects an extremely fine droplet. The vacuum caused by the decrease in pressure creates a new bubble.

Generally, we make a distinction between the two different technologies:

•

Inkjet printers use nozzles that have their own built-in heating element. Thermal technology is used here.

•

Bubble jet printers use nozzles that have piezoelectric technology. Each nozzle works with a piezoelectric crystal that changes shape when excited by its resonance frequency and ejects an ink bubble.

Laser Printer The laser printer produce quality print-outs inexpensively at a high print speed. However, these printers are mostly used in professional and semi-professional settings because of their high cost. Laser printers use a technology that is close to that used by photocopiers. A laser printer is mainly made up of an elecrostatically charge photosensitive drum that attracts the ink in order to make a shape that will be deposited on the sheet of paper. How it works: a primary charge roller gives the sheets of paper a positive charge. The laser gives a positive charge to certain spots on the drum with a pivoting mirror. Then, negatively charged ink in powder form (toner) is deposited on the parts of the drum that were previously charged by the laser. By turning, the drum deposits the ink on the paper. A heating wire (called a corona wire) finally attaches the ink to the paper.

Because laser printers do not have mechanical heads, they are quick and quiet. There are two different types of laser printer technology: "carousel" (four passes) or "tandem" (single-pass). •

carousel: with carousel technology, the printer passes over the paper four times to print a document (one for each primary colour and one for black, which in theory makes printing in colour four times slower than in black).

•

tandem: a laser printer using "tandem" technology deposits each colour in one single pass. The toners are deposited simultaneously Output is as fast when printing in colour as it is when printing in black. However, this technology is more expensive because the mechanics behind it are more

complicated. Therefore it is used only by middle to top-of-the-line colour laser printers. LED Printer Another printer technology competes with laser printers: LED (Light Emitting Diode) technology. With this technology, an electroluminescent diode printhead polarises the drum with a very fine light ray, making very small dots. This technology is particularly well adapted for obtaining high resolutions (600, 1,200 or 2,400 dpi). Given that each diode is makes one point, print speed hardly affects resolution. Moreover, this technology lacks moving parts, which translates into less-expensive and more solid and reliable printers. Printer Command Language Page description language is the standard language that computers use to communicate with printers. Indeed, a printer must be able to interpret the information that a computer is sending to it. The two main page description languages are: •

Printer command language (PCL): a language made up of binary sequences. The characters are transmitted according to their ASCII code

•

PostScript language: this language, originally used for Apple LaserWriters, has become the standard in page description languages. It is a language in its own right based on a set of instructions

Print Servers There are control boxes called print servers that allow you to make a printer with a USB or parallel connection available to a whole network. The Scanner

NextModem

The Scanner A scanner is an acquisition peripheral for scanning documents, i.e. converting a paper document to a digital image. There are generally three types of scanner: •

Flat scanners let you scan a document by placing it flat against a glass panel. This is the most common type of scanner.

•

Hand scanners are smaller in size. These scanners must be moved manually (or semi-manually) in successive sections over the document in order to scan the whole document.

•

Sheet-fed scanners feed the document through a lighted slot in order to scan them, similar to fax machines. This type of scanner is increasingly built into machines such as multi-function printers.

There are also scanners that are able to scan specific items such as slides.

Characteristics of a scanner A scanner is generally characterised by the following elements: •

Resolution: expressed in dots per inch (referred to as dpi), the resolution defines the fineness of the scan. The order of magnitude of the resolution is around 1200 per 2400 dpi. The horizontal resolution is very much dependent on the quality and number of captors, whereas vertical resolution is closely linked to the accuracy of the drive motor. However it is important to distinguish the optical resolution, which is the actual resolution of the scanner, from the interpolated resolution. Interpolation is a technique involving defining intermediate pixels from among actual pixels, by calculating the mean of the colours of neighbouring pixels. This technology helps achieve good results but the interpolated resolution thus defined is in no way a criterion that can be used to compare scanners.

•

The format of the document: depending on their size, scanners are able to accommodate documents of different sizes, generally A4 (21 x 29.7 cm), or more rarely A3 (29.7 x 42 cm).

•

Acquisition speed: expressed in pages per minute (ppm), the acquisition speed represents the scanner's ability to pick up a large number of pages per minute. The acquisition speed depends on the document format and the resolution chosen for the scan.

•

Interface: this is the scanner connector. The main interfaces are as follows: o

FireWire. This is the preferred interface since its speed is particularly suited to this type of peripheral

o

USB 2.0. This is offered on all recent computers. It is a standard interface which is recommended if the computer has no FireWire connection

o

SCSI. Preferred interface for the scanner at the end of the 90s, the SCSI standard has now been abandoned in favour of the FireWire and the USB 2.0

o

Parallel port. This type of connector is naturally slow and is used less frequently; it should be avoided if the computer has one of the preceding connectors

•

Physical characteristics: other elements may be taken into account when choosing a scanner: o

Size, in terms of the physical dimensions of the scanner.

o

Weight.

o

Electricity consumption, expressed in Watts (W).

o

Operating and storage temperatures.

o

Noise level. Scanners can be very noisy, and this may cause considerable disturbance.

o

Accessories: The drivers and user manual are usually provided, but you must check that connection cables are also provided; if not they must be purchased separately.

How a scanner works The operating principle for a scanner is as follows: •

The scanner moves over the document line by line

•

Each line is broken down into "basic dots" which correspond to pixels.

•

A captor analyses the colour of each pixel

•

The colour of each pixel is broken down into 3 components (red, green, blue)

•

Each colour component is measured and represented by a value. For 8-bit quantification, each component will have a value between 0 and 225 inclusive.

The rest of this article will specifically describe the operation of a flat scanner, although the operating mode for a hand scanner or sheet-fed scanner is exactly the same. The only difference is in the feeding of the document. A flat scanner has a motor-driven lighted slot which scans the document line by line under a transparent glass panel on which the document is placed, with the scanning side face down. The high-intensity light emitted is reflected by the document and converges towards a series of captors via a system of lenses and mirrors. The captors convert the light intensities received into electrical signals, which are in turn converted into digital data by an analogue-digital converter. There are two categories of captors: •

CMOS captors (Complementary Metal Oxide Semi-conductor), or Complementary MOS). This is known as the CIS technology (Contact Image Sensor). This type of device uses an LED ramp (Light Emitting Diode) for lighting the document and requires a very close distance between the captors and the document. The CIS technology, however, uses a lot less energy.

•

CCD captors (Charge-coupled devices). Scanners using CCD technology are often thicker as they use a cold neon lamp. The quality of the scanned image is on the whole better however, since the signal/noise ratio is lower.

Modem

NextGraphics card

What is a Modem used for? A modem is the peripheral used to transfer information between several computers over a wire transmission medium (e.g. telephone lines). Computers operate digitally using binary language (a series of zeros and ones), but modems are analogue. The digital signals pass from one value to another. There is no middle or half-way point. It is "All or Nothing" (one or zero). On the other hand, analogue signals do not move "in steps", but rather continuously.

For example, a piano works more or less digitally because there are no "steps" between notes. Conversely, a violin can modulate its notes to pass through all possible frequencies. A computer operates like a piano and a modem like a violin. The modem converts binary information from the computer into analogue information in order to modulate it over the telephone line. You can hear bizarre noises if you turn up the sound from the modem. Thus, a modem modulates digital information on analogue waves. In the opposite direction, it demodulates analogue data in order to convert them into digital data. The word "modem" is an acronym for "MOdulate/DEModulate".

A modem's transmission speed is generally expressed in bauds, in tribute to Emile Baudot (11 September 1845 - 28 March 1903), a famous French engineer who worked in the area of telecommunications. This unit of transmission speed characterises the frequency of (de)modulation, i.e. the number of times the modem makes the signal change status per second. Thus, the bandwidth in bauds is not quite equal to the bandwidth in bits per second because a signal status change may be necessary to encode a bit. Communication Standards As modems proliferated, the need increased for standardised protocols for communication by modem, so that all the protocols would use a common language. This is why two organisations developed communication standards: •

The BELL laboratories, precursors in the area of telecommunications

•

The International Telephone and Telegraph Consultative Committee (CCITT), known since 1990 as the International Telecommunication Union (ITU).

The goal of the ITU is to define international communications standards. Modem standards can be divided into 3 categories: •

Modulation standards (e.g. CCITT V.21)

•

Error correction standards (e.g. CCITT V.42)

•

Data compression standards (e.g. CCITT V.42bis)

Here is a list of the main modem standards: Modulation Theoretical Standard Bandwidth

Mode Description

Bell 103

Full An American and Canadian standard that uses audio frequency-shift duplex keying to encode data. This allows one bit to be sent per baud.

300 bps

CCITT V.21 300 bps

Full An international standard similar to the Bell 103 standard. duplex

Bell 212A

1,200 bps

Full An American and Canadian standard that uses differential phase-shift duplex keying to encode data. This standard allows 2 bits to be sent per baud.

ITU V.22

1,200 bps

Half An international standard close to the Bell 212A standard. duplex

ITU V.22bis 2,400 bps

Full An international standard that is an improved version of the V.22 duplex standard (thus the name V.22bis).

ITU V.23

1,200 bps

An international standard that transmits data in half-duplex mode, i.e. Half data is transmitted in just one direction at a time. Optional 75 baud duplex reverse channel.

ITU V.23

An international standard giving asymmetrical full duplex, i.e. it 1,200 bps/75 Full allows data transmission in one direction at 1,200 bps and at 75 bps in bps duplex the other direction.

ITU V.29

9,600 bps

An international standard that transmits data in half-duplex mode, i.e. Half data is transmitted in just one direction at a time. This standard was duplex developed especially for fax machines.

9,600 bps

An international standard that transmits in full-duplex mode and incorporates error correction standards. Data transmission takes place Full according to an error correction technique called quadrature duplex amplitude trellis-coded modulation. This technique consists in sending an additional bit for each group of 4 bits that are sent on the transmission line.

ITU V.32

ITU V.32bis 14,400 bps

An international standard that improves on the v.32 standard by Full allowing 6 bits per baud to be sent and a transmission speed of up to duplex 14,400 bps.

ITU V.32fast 28,800 bps

Full An international standard sometimes called V.FC (Fast Class) that duplex allows data transmission at a speed of 28,800 bps.

ITU V.34

28,800 bps

An international standard that allows data transfer at 28,800 bps. Full Thanks to a DSP processor (Digital Signal Processor), modems using duplex this standard can attain a speed of up to 33,600 bps.

ITU V.90

56,000 bps

Full An international standard that allows transmission speeds of up to duplex 56,000 bps.

Graphics cards - Video cards

NextSound card

2D Accelerator Cards A graphics card, sometimes called a graphics adapter, video card or graphics accelerator, is a computer component which converts digital data into a graphical form which can be displayed on a monitor. The initial role of a graphics card was to send pixels to a screen, as well as a variety of simple graphical manipulations: •

Moving blocks (such as the mouse cursor);

•

ray tracing;

•

polygon tracing;

•

etc.

More recent graphics cards now have processors built for handling complex 3D graphical scenes.

A video card's main components are: •

A Graphical Processing Unit (or GPU for short), the heart of a graphics card, which processes images based on the encoding being used. The GPU is a specialised processor with advanced image processing capabilities, especially for 3D graphics. Because of the high temperatures that the graphics processor can reach, a radiator and fan are often mounted on it.

•

The job of the video memory is to store images processed by the GPU before they are displayed by the monitor. The larger the video memory, the better the graphics card can handle textures when displaying 3D scenes. The term frame buffer is generally used to refer to the part of the video memory which stores images before they are shown onscreen. Graphics cards rely heavily on the type of memory that the card uses, as their response time is crucial for displaying images quickly, as is the amount of memory, which affects the number and resolution of the images that may be stored in the frame buffer.

•

The RAMDAC (random access memory digital-analog converter) is used for converting digital images stored in the frame buffer as analog signals to send to the monitor. The RAMDAC's frequency determines the refresh rate (number of images per second, expressed in Hertz - Hz) that the graphics card can support.

•

The video BIOS contains the graphics card's settings, in particular the graphics modes that the adapter supports.

•

The interface: This is a kind of bus used to connect the graphics card to the motherboard. The AGP bus is specifically designed to handle high dataflow,

which is necessary when displaying video or 3D sequences. The PCI Express bus performs better than the AGP bus that it has ended up replacing. •

The connections: o

Standard VGA interface: Most graphics cards are built with a 15-pin VGA (Mini Sub-D, with 3 rows of 5 pins each), usually coloured blue, which is mainly used to connect the adapter to a CRT monitor. This type of interface is used to send 3 analog signals to the screen, corresponding to the red, blue, and green components of the image.

o

The DVI (Digital Video Interface), found in some graphics cards, is used to send digital data to monitors which can support the interface. This bypasses the need to convert digital data into analog and then back again.

o

S-Video interface: More and more graphics cards these days have an S-Video socket built in, so that the computer's output can be viewed on a television screen. This is why it is often called a "TV-out" plug.

3D Accelerator Cards The field of 3D is much more recent, and is becoming more important. Some PCs can now compute faster than certain workstations. Computing a 3D scene is a process which is roughly divided into four steps: •

script: laying out elements

•

geometry: creating simple objects

•

setup: cutting the objects into 2D triangles

•

rendering: applying textures to the triangles.

The better the 3D accelerator card can compute these steps by itself, the faster it can be displayed. The first chips could only render, letting the processor take care of the rest. Since then, graphics cards have included a "setup engine", which handles both of the last two steps.

For example, a 266 Mhz Pentium II which computes the first three steps can process 350,000 polygons per second; when it only computes two, it can reach 750,000 polygons per second. This demonstrates how much of a load these cards remove from the processor. The type of bus is also an important factor. While an AGP bus doesn't improve 2D images, cards that use that bus instead of the PCI bus are higher-performance. This is due to the fact that an AGP bus is directly linked to the RAM, which gives it much higher bandwidth than a PCI bus. These high-technology products now require the same manufacturing quality as processors do, as well as etching between 0.25 µm and 0.35 µm in width. Glossary of 3D and 2D accelerator functions Term

Definition

2D Graphics

Displaying a representation of a scene using two reference axes (x and y)

3D Graphics

Displaying a representation of a scene using three reference axes (x, y and z)

The world is made up of opaque, translucent, and transparent objects. Alpha blending is a way to add transparency data to translucent objects. This is done by rendering polygons through masks whose density is proportional to the objects' transparency. The resulting Alpha blending pixel's colour is a combination of the foreground and background colours. The alpha's value is generally between 0 and 1, calculated as follows: new pixel=(alpha)*(colour of first pixel)+(1-alpha)*(colour of second pixel) Alpha buffer

Anti-aliasing

This is an additional channel for storing transparency information (Red, Green, Blue, Transparency). A technique for making pixels appear smoother.

Atmospheric effects

Effects like fog or depth, which improve the rendering of an environment.

Bitmap

Pixel-by-pixel image

Bilinear filtering

Used for making a pixel look more fluid when it moves from place to place (such as when rotated)

BitBLT

This is one of the most important acceleration functions, which simplifies the act of moving data blocks, by taking into account the specific features of the video memory. It is used, for example, when a window is moved.

Blending

Combining two images by adding them bit-by-bit to one another.

Bus Mastering

A PCI bus function which is used to directly receive information from the memory without going through the processor

Perspective correction

A texture mapping method. It takes the Z value into consideration when mapping polygons. When an object extends into the distance, it appears to diminish in height and width. Perspective correction involves making sure the rate at which the texture's pixels change size is proportionate to depth.

Depth Cueing

Lowers the intensity of objects extending into the distance

Dithering

Used for storing 24-bit quality images in smaller buffers (8 or 16 bits). Dithering combines two colours to make one.

Double buffering

A method which uses two buffers, one for the display, and the other for rendering, so that when the render is done the two buffers are switched.

Flat shading or Constant Assigns a solid colour to a polygon. The object rendered this way looks faceted. shading Fog

Uses the blending function for a fixed-colour object (the further it recedes into the background, the more heavily this feature is used)

Gamma

The characteristics of a monitor that uses phosphorus are non-linear: A slight change in voltage at a low voltage changes the brightness of the monitor, while the same change at a high voltage will not result in the same magnitude of brightness. The difference between what is expected and what is observed is called Gamma.

Gamma Correction

Before being displayed, the data must be corrected to compensate for the Gamma effect.

Gouraud Shading

An algorithm (named after the French mathematician who invented it) which uses interpolation to smooth out colours. It assigns a colour to each pixel in a polygon based on interpolating the colours at its vertices, in order to simulate the appearance of plastic or metallic surfaces.

Interpolation

Mathematical method for inferring missing or damaged information. For example, when an image in enlarged, the missing pixels are regenerated by interpolation.

Line Buffer

A buffer created to store a video line.

An algorithm (named after Phong Bui-Tong) for shading colours by computing the amount Phong Shading of light that would strike various points on an object's surface, and then changing the colour of the pixels based on those values. It uses more resources than Gouraud shading.

MIP Mapping

This is a word which comes from the Latin "Multum in Parvum", meaning "many in one". This method is used to apply textures with different resolutions to objects within a single image, depending on their size and distance. Among other things, this lets higherresolution textures be used when the object gets nearer.

Projection

This is the act of transforming a 3-dimensional space into a 2-dimensional space.

Rastering

Turning an image into pixels

Rendering

This is the act of creating realistic images on a screen by using mathematical models for smoothing, colouring, etc.

Rendering engine

Hardware or software used for computing 3D primitives (generally triangles).

Tesselation or facetting

The act of 3D graphics computing can be divided into 3 parts: Facetting, geometry, and rendering. The step called facetting involves cutting a surface into smaller shapes (often triangles or quadrilaterals)

Texture Mapping

Involves storing images made of pixels (texels), then wrapping 3D objects in this texture for more realistic-looking objects.

Tri-linear filtering

Based on the principle of bi-linear filtering, tri-linear filtering involves averaging two levels of bi-linear filtering

Z-buffer

The part of memory which stores the distance of each pixel from observer. When objects are rendered onscreen, the rendering engine must delete unseen surfaces.

Z-buffering

The act of deleting hidden faces by using the values stored in the Z-buffer.

Sound card

NextNetwork adapter

Introduction to sound cards The sound card (also called an audio card) is the part of a computer which manages its audio input and ouput.

It is usually a controller which can be inserted into an ISA slot (or PCI for more recent ones), but more and more motherboards include their own sound card. Sound card connectors The main components of a sound card are: •

The specialised processor, called the DSP (digital signal processor), which does all the digital audio processing (echo, reverb, vibrato chorus, tremelo, 3D effects, etc.);

•

The digital to analog converter, or DAC for short, which converts the computer's audio data into an analog signal for being sent to a sound system (such as speakers or an amplifier);

•

The analog to digital converter, or ADC for short, which converts an analog input signal into digital data which a computer can process;

•

External input/output connectors: o

On or two standard 3.5 mm line-out jacks, normally light green in colour;

o

A line-in jack;

o

A microphone input (sometimes called Mic), usually a pink-coloured 3.5 mm jack;

o

An SPDIF digital output (Sony Philips Digital Interface, also known as S/PDIF or S-PDIF or IEC 958 or IEC 60958 since 1998). This is an output line which sends digitised audio data to a digital amplifier using a coaxial cable with RCA connectors at the ends.

o

A MIDI connector, usually gold-coloured, which is used for connecting musical instruments, and can serve as a game port for plugging in a

controller (like a joystick or gamepad) which has a SUB-D 15-pin connector. •

Internal input/output connectors: o

A CD-ROM/DVD-ROM connector, with a black socket, which is used to connect the sound card into a CD-ROM's analog audio output using a CD Audio cable;

o

Auxiliary inputs (AUX-In), with white sockets, used for connecting internal audio sources such as a TV tuner card;

o

Telephone answering device connectors (TAD), which have a green connector.

Network cards

NextBIOS

What is a network card? A network card (also called a Network Adapter or Network Interface Card, or NIC for short) acts as the interface between a computer and a network cable. The purpose of the network card is to prepare, send, and control data on the network.

A network card usually has two indicator lights (LEDs): •

The green LED shows that the card is receiving electricity;

•

The orange (10 Mb/s) or red (100 Mb/s) LED indicates network activity (sending or receiving data).

To prepare data to be sent the network card uses a transceiver, which transforms parallel data into serial data. Each cart has a unique address, called a MAC address, assigned by the card's manufacturer, which lets it be uniquely identified among all the network cards in the world. Network cards have settings which can be configured. Among them are hardware interrupts (IRQ), the I/O address and the memory address (DMA). To ensure that the computer and network are compatible, the card must be suitable for the computer's data bus architecture, and have the appropriate type of socket for the cable. Each card is designed to work with a certain kind of cable. Some cards include multiple interface connectors (which can be configured using jumpers, DIP switches, or software). The most commonly used are RJ-45 connectors.

Note: Certain proprietary network topologies which use twisted pair cables employ RJ-11 connectors. These topologies are sometimes called "pre-10BaseT ". Finally, to ensure that the computer and network are compatible, the card must by compatible with the computer's internal structure (data bus architecture) and have a connector suitable for the kind of cabling used. What is the role of a network card? A network card is the physical interface between the computer and cable. It converts the data sent by the computer into a form which can be used by the network cable, transfers that data to another computer and controls the dataflow between the computer and cable. It also translates the data coming from the cable into bytes so that the computer's CPU can read it. This is why a network card is an expansion card inserted into an expansion slot. Preparing data The paths taken by data moving with a computer are called "buses". Multiple sideby-side paths force data to move in parallel, and not in series (one after another). •

The first buses transported 8 bits at a time.

•

IBM's PC/AT computer introduced the first 16-bit buses.

•

Today, most buses are 32-bit.

However, data travels on cables in series (only one channel), moving in only one direction. The computer can send OR receive data, but cannot do both at once. For this reason, the network card restructures a group of data arriving in parallel into a serial (1-bit) data stream. To do so, the digital signals are transformed into electrical or optical signals which can travel over network cables. The device that translates them is called the transceiver. The role of the identifier •

The card converts data and notifies the rest of the network of its address, so that it can be told apart from the other network cards.

•

MAC addresses: Defined by the IEEE (Institute of Electrical and Electronics Engineer), which assigns ranges of addresses to each manufacturer of network cards.

•

They are inscribed on the cards' chips, and as a result, each card has a unique MAC address on the network.

Other network card functions The computer and the card must communicate so that data can travel between them. For this reason, the computer assigns part of its memory to cards that include DMA (Direct Access Memory). The interface card indicates that another computer is requesting data from that computer. The computer's bus transfers the data from the computer memory to the network card.

If the data is moving too fast for the adapter to process, they are placed in the card's buffer memory (RAM), where they are temporarily stored while the data is being sent and received. Sending and controlling data Before the sending network card transmits its data, it interacts electronically with the receiving card to resolve the following issues: •

Maximum size of data blocks that will be sent

•

Amount of data to send before confirmation

•

Intervals of time between partial data transmissions

•

Waiting period before sending confirmation

•

Volume of data that each card may build up before releasing it to its CPU

•

Data transmission speed

If a more recent, advanced card communicates with a slower one, they still have to share the same transmission speed. Some cards have circuits for adjusting themselves to the transfer speeds of a slower card. Both cards must accept and adjust to the other card's settings before data can be sent and received. Network card configuration settings Network adapters have configuration options: Among others: •

Interruption (IRQ): In most cases, network cards use IRQ 3 and 5. IRQ 5 is recommended (whenever available) and most cards use it as the default setting.

•

Input/Output (I/O) base address: Each device must have a different address for the corresponding port.

•

Memory address: This designates a RAM location in the computer. The network card uses this slot as a buffer for data entering and leaving. This setting is sometimes called the RAM Start Address. In general, a network card's memory address is D8000. The last 0 is left out on some network cards. You have to be careful not to select an address already being used by another device. It should, however, be noted that some network cards have no configurable memory address because they don't use the machine's RAM addresses.

•

The transceiver

Note: The card can be configured using software. The settings have to match the placement of the jumpers or the DIP (Dual Inline Package) switches found on the network card. These settings are provided with the card's documentation. Many recent cards use PnP (Plug and Play). This means that the card does not need to be manually configured, but sometimes can cause hardware conflicts; when this happens, it is helpful to disable the PnP option and configure the card "by hand." BIOS

Introduction to BIOS BIOS ("Basic Input/Output System" is an essential component in computers, which is used for controlling hardware. It is a small software program, part of which is loaded in ROM (read-only memory, which cannot be modified), and part of which is in EEPROM (electrically erasable programmable read-only memory, hence the term Flashing to indicate the action to change the EEPROM). The POST When a computer system is turned on or reset, the BIOS does an inventory of the hardware found on the computer and carries out a test (called POST for "Power-On Self Test") in order to verify that all of it is functioning properly. •

Testing the processor (CPU)

•

Checking the BIOS

•

Checking CMOS configuration

•

Initialising the timer (the internal clock)

•

Initialising the DMA controller

•

Checking RAM and cache memory

•

Installing all BIOS functions

•

Checking all configurations (such as the keyboard, disk drives, and hard drives)

If the POST discovers an error, it will attempt to continue booting the computer. However, if the error is serious, the BIOS will stop loading the system and: •

display a message on the screen, if possible (as the display device might not yet have been initialised, or might be defective);

•

emit a sequence of beeps, which refer to the source of the error;

•

send a code (called the POST code) to the computer's serial port, which may be retrieved using special diagnostic hardware.

If everything is correct, the BIOS will usually play a short beep to report that there are no errors.

Meaning of beeps in recent Award BIOS systems # of beeps 1 short beep

Meaning PC is booting normally

How to resolve the problem

2 short beeps

CMOS problem

Reinitialise the CMOS by removing the BIOS stack and replacing it, or by moving jumper JP4

1 long beep / 1 short beep

Problem with motherboard or RAM

Place RAM modules correctly in slot, test RAM or change it

1 long beep / 2 short beeps

Problem with graphics Check that the graphics card is correctly placed in its slot. If need card be, test with another video card.

1 long beep / 3 short beeps

Problem with keyboard

Check that the keyboard is correctly plugged in, and that no keys are depressed. If need be, test with another keyboard.

1 long beep / 9 short beeps

BIOS failure

The BIOS is invalid, replace it with a more recent version

3 beeps

Base 64K RAM failure RAM contains errors. Try reinserting it correctly or replacing it.

4 beeps

Refresh error

RAM is not refreshing correctly. Reset the refresh values in the BIOS or reset the BIOS.

5 beeps

Processor error

Check that the processor is correctly plugged in, and that the fan is working. If need be, change it.

6 beeps

Problem with keyboard

Check that the keyboard is correctly plugged in, and that no keys are depressed. If need be, test with another keyboard.

8 beeps

Problem with graphics Check that the graphics card is correctly placed in its slot. If need card be, test with another video card.

Long incessant beeps

RAM error

Place RAM modules correctly in slot, test RAM or change it

Short incessant beeps

Power supply error

Check that all power cables are correctly connected to the motherboard, test with another power supply, or change them

Meaning of beeps for an AMI BIOS # of beeps

Meaning

How to resolve the problem

1

Refresh failure

RAM is not refreshing correctly. Reset the refresh values in the BIOS or reset the BIOS. Place RAM modules correctly in slot, or change them.

2

Parity Error

Place RAM modules correctly in slot, or change them. Test the RAM.

3

Base 64K RAM failure

Place RAM modules correctly in slot, or change them. If need be, update the BIOS.

4

System timer not operational

The motherboard must be sent for repairs.

5

Processor Error

Check that the processor is correctly plugged in, and that the fan is working. If need be, change it.

6

Gate A20 failure

Check that the keyboard is correctly plugged in, and that no keys are

depressed. If need be, test with another keyboard. 7

Processor exception interrupt error

The motherboard must be sent for repairs.

8

Display memory read/write failure

Check that the graphics card is correctly placed in its slot. If need be, test with another video card.

9

ROM checksum error

The BIOS chip must be replaced or updated.

10

CMOS shutdown The motherboard must be sent for repairs. register read/write error

11

Check that the processor is correctly plugged in, and that the fan is Cache memory problem working. If need be, change it. Place the RAM modules correctly in their slots, or replace them.

Meaning of beeps in a Phoenix BIOS # of beeps

Meaning

How to resolve the problem

1-3-1-1

DRAM Refresh error

Place the RAM modules correctly in their slots, or replace them.

1-2-2-3

ROM checksum error

Place the RAM modules correctly in their slots, or replace them.

1-3-1-3

Keyboard Controller Error Place the keyboard correctly in its slot, or replace it.

1-3-4-1

RAM error

Place the RAM modules correctly in their slots, or replace them.

1-3-4-3

RAM error

Place the RAM modules correctly in their slots, or replace them.

1-4-1-1

RAM error

Place the RAM modules correctly in their slots, or replace them.

2-2-3-1

Unexpected interrupt

For an Award BIOS, only video-related errors will trigger beeps. Other errors are sent as POST codes and are displayed onscreen. For example, a long beep, followed by two short beeps, indicates an error in a video device (graphics card). In such a case, you will have to try to place the video card in its slot correctly, or replace it altogether. Any other beep indicates a memory-based error. Here is the list of POST codes, and the meaning of beep sequences for each of the three main BIOS manufacturers: •

Phoenix - Phoenix BIOS POST code

•

AMIBIOS - AMIBIOS POST code

•

Award - BIOS Award POST code

BIOS setup Most BIOSes have a setup program for modifying basic system configurations. This kind of information is stored in self-powered memory (using a battery) so that the data remains saved even when the computer is off (RAM is reinitialised each time the system boots). Each machine has several BIOSes: •

The motherboard BIOS

•

The BIOS which controls the keyboard

•

The video card BIOS

•

and possibly o

the BIOS for SCSI controllers, used for booting from the SCSI device, which then communicate with the DOS without requiring an additional driver

o

(The network card BIOS for booting from the network)

When the computer is turned on, the BIOS displays a copyright message on the screen, then carries out diagnostic and initialisation tests. After these tests are complete, the BIOS displays a message prompting the user to press one or more keys in order to enter BIOS setup. Depending on what brand of BIOS it is, it may be the F2 key, the F10 key, the DEL key, or one of the following key sequences: •

Ctrl+Alt+S

•

Ctrl+Alt+Esc

•

Ctrl+Alt+Ins

On Award BIOSes, the following message is displayed during POST: TO ENTER SETUP BEFORE BOOT PRESS CTRL-ALT-ESC OR DEL KEY

Reinitialising the BIOS As BIOS setup is used to edit hardware settings, changing them might cause the system to become unstable, and it might not even restart. When this happens, the changes to the BIOS must be cancelled, and the default settings must be restored. If the computer boots up and you can access the BIOS, it will usually allow you to return to the default settings. In PhoenixBIOS, press F9 to return the configuration to the defaults set by the manufacturer. In AwardBIOS, press F9 to restore the previous settings, F6 to restore Award BIOS's default settings, and F7 to restore the

defaults

set

by

the

motherboard's

manufacturer.

If you cannot access the BIOS using standard procedures, most motherboards include a jumper for resetting the default values. Simply change the jumper's position, then leave it there for about ten seconds. It is strongly recommended to shut off the computer's power before making these changes. Whenever doing so, refer to the manual that came with your motherboard.

Cables and connectors

NextDB-9

Connectors

In information science, connectors, normally called "input-output connectors" (or I/O for short), are interfaces for linking devices by using cables. They generally have a male end with pins protruding from it. This plug is meant to be inserted into a female part (also called a socket), which includes holes for accommodating the pins. However, there are "hermaphroditic" plugs which can act as either male or female plugs, and can be inserted into either one. Pin layout

The pins and holes in connectors are usually linked to the electric wires which form the cable. The pin layout describes which pins couple with which wires. Each numbered pin generally corresponds to a wire within the cable, but sometimes one of the pins is left unused. Additionally, in some cases, two pins may be linked to one another; this is called a "bridge." Input/output connectors

The computer's motherboard has a certain number of input-ouput connectors located on the "rear panel."

Most motherboards have the following connectors: • • • •

• •

Serial port, which uses a DB9 connector, for connecting older devices; Parallel port, which uses a DB25 connector, mainly for connecting old printers; USB ports (1.1, low-speed, or 2.0, high-speed), for connecting more recent peripherals; RJ45 connector (called the LAN port or Ethernet port), for connecting the computer to a network. It interfaces with a network card built into the motheboard; VGA connector (called SUB-D15), used for hooking up a monitor. This connector interfaces with the built-in graphics card; Jacks (Line-In, Line-Out and microphone), for connecting speakers or a hi-fi sound system, as well as a microphone. This connector interfaces with the built-in sound card.

DB9 connector

NextDB-25

DB9 connector

The DB9 (originally DE-9) connector is an analog 9-pin plug of the DSubminiature connector family (D-Sub or Sub-D). The DB9 connector is mainly used for serial connections, allowing for the asynchronous transmission of data as provided for by standard RS232 (RS-232C).

Note that there are DB9-DB25 adapters for easily converting a DB9 plug into a DB25, and vice versa. Pins

Pin number

Name

1

CD - Carrier Detect

2

RXD - Receive Data

3

TXD - Transmit Data

4

DTR - Data Terminal Ready

5

GND - Signal Ground

6

DSR - Data Set Ready

7

RTS - Request To Send

8

CTS - Clear To Send

9

RI - Ring Indicator Shield

Last update on Thursday October 16, 2008 02:43:14 PM

DB25 connector

NextPS/2

DB25 plugs

The DB25 (originally DE-25) connector is an analog 25-pin plug of the D-Subminiature connector family (D-Sub or Sub-D). As with the DB9 connector, the DB25 is mainly used for serial connections, allowing for the asynchronous transmission of data as provided by standard RS-232 (RS-232C). It is also used for parallel port connections, and was originally used to connect printers, and as a result is sometimes known as a "printer port" (LPT for short). So to avoid confusion, DB25 serial ports on computer generally have male connectors, while parallel port connectors are DB25 female plugs.

Pins (serial connection)

Pin number

Name

2

TXD - Transmit Data

3

RXD - Receive Data

4

RTS - Request To Send

5

CTS - Clear To Send

6

DSR - Data Set Ready

7

GND - Signal Ground

8

CD - Carrier Detect

20

DTR - Data Terminal Ready

22

RI - Ring Indicator

Pins (parallel connection)

Pin number

Name

1

_STR - Strobe

2

D0 - Data bit 0

3

D1 - Data bit 1

4

D2 - Data bit 2

5

D3 - Data bit 3

6

D4 - Data bit 4

7

D5 - Data bit 5

8

D6 - Data bit 6

9

D7 - Data bit 7

10

ACK - Acknowledgement

11

Busy

12

Paper Out

13

Select

14

Auto feed

15

Error

16

Reset

17

Select Input

18

Ground

19

Ground

20

Ground

21

Ground

22

Ground

23

Ground

24

Ground

25

Ground

PS/2 connector

NextUSB

PS/2 connector

The PS/2 connector (mini-DIN6 format) is mainly used to connect computers to keyboards and mice.

Pins

Pin number

Function

1

Clock

2

Ground

3

Data

4

Ground (or not connected)

5

+ 5V

6

Not connected

USB/USB 2.0 connector

NextFirewire

USB Connectors

USB (Universal Serial Bus) is an input-output interface which is much faster than standard serial ports. There are two kinds of USB connectors: •

•

"Type A" connectors, which are rectagular in shape and are generally used for devices which consume little bandwidth (like keyboards, mice, and webcams); "Type B" connectors, which are square-shaped and are generally used for devices with heavy bandwidth requirements (like external hard drices);

Pins

The pins on a USB connector are as follows: Pin number

Function

1

Power supply +5V (VBUS) 100mA maximum

2

Data (D-)

3

Data (D+)

4

Ground (GND)

Last update on Thursday October 16, 2008 02:43:14 PM

FireWire connector

NextJack

FireWire connector (IEEE 1394)

The IEEE 1394 bus (named after the standard that applies to it) was released in late 1995 to provide a way to send data over a connection at high speeds. Apple gave it the brand name "FireWire", which has stuck. Sony released it as i.Link, while Texas Instruments called it Lynx. FireWire is a port found on some computers for connecting peripheral devices (especially digital cameras) at very high speeds. There are different FireWire connectors for each IEEE 1394 standard.

•

The IEEE 1394a standard defines two connectors: o connectors 1394a-1995 :

o

•

1394a-2000 connectors, called mini-DV, as they are used in some DV (Digital Video) cameras:

IEEE 1394b defines two types of connector designed so that 1394b Beta plugs can be plugged into both Beta and Bilingual connectors, but 1394b Bilingual can only be plugged into Bilingual connectors: o 1394b Beta connectors:

o

1394b Bilingual connectors:

Pins on a FireWire connector

The pins on a FireWire are as follows: #

6 wires

4 wires

1 VCC (12V) TPB2 Ground (0V) TPB+ 3 TPB-

TPA-

4 TPB+

TPA+

5

TPA-

6

TPA+

Jack

NextDIN

Jack

The "jack" is without a doubt the most commonly used connector for small-scale audio equipment. Jacks are normally divided into three different types, based on their diameter: • • •

2.5 mm jack: The smallest jack; 3.5 mm jack: The traditional jack, which corresponds to a headphone jack; 6.35 mm jack: The jack used for semi-professional sound systems, in order to connect speakers, amplifiers, or microphones.

There are two versions of each of these jacks: •

•

Mono jacks, for sending monophonic sound. This kind of jack has two contacts: a reference, found on the body of the cord, and the signal on the tip. Stereo jacks, for sending stereophonic sound. This kind of jack has three contacts: The same two as its mono counterpart, as well as an additional ring for sending another audio channel.

In computer sound cards, the plugs for jacks are generally colourcoded so users can easily tell which type of audio device each one connects to, and whether they are audio inputs or outputs.

Last update on Thursday October 16, 2008 02:43:14 PM Nextmini-DIN

Types of connectors 5-pin DIN plugs

A DIN (or DIN5) connector is a plug with 5 pins, formerly used to connect keyboards to computers:

The DIN5 connector has been made obsolete by PS/2 and USB connectors. Pins

Pin number

Function

1

Reset (_RST)

2

+ 5 V (power)

3

Data

4

Ground

5

Clock

Last update on Thursday October 16, 2008 02:43:14 PM NextVGA (Sub-D15)

Mini-DIN connector 4-pin Mini-DIN connector

The 4-pin Mini-DIN connector is used for transmitting analog video in S-Video format:

More and more graphics cards these days have an S-Video socket built in, so that the computer's output can be viewed on a television screen. This is why it is often called a "TV-out" plug.

VGA (SUB-D15) connector

NextRCA (Cinch)

SUB-D15 plugs

Mini Sub-D (ou SUB-D15) is a 15-pin connector (with three rows of 5 pins each). This kind of connector is built into most graphics cards and is used to send 3 analog signals to the monitor, which correspond to the red, blue, and green components of the image:

The graphics card's VGA conector is usually blue:

Last update on Thursday October 16, 2008 02:43:14 PM NextTOSlink

RCA connectors (CINCH) RCA connector

The RCA connector (Radio Corporation of America, sometimes called CINCH) is a connector used for transporting audio or video signals. The RCA plug is used to send video and audio signals (in mono or stereo) through a two-wire cable, with either an analog or digital transmission method. The connector's colour indicates how it is meant to be used. For stereo analog audio transmissions, the connectors are red and white:

For a composite video signal, the connector is yellow:

The RCA connector is also used for sending component video, also called YUV or YCrCb. For such a video signal, 3 connectors, coloured red, green, and blue, are used:

Last update on Thursday October 16, 2008 02:43:14 PM NextSCART

TOSLink Plug TOSLink Plug

The TOSLink connector (TOShiba LINK, named for the company that created it) is an optical connector for sending audio or video data over a fibre-optic cable:

The data is transmitted using visible optical signals sent by a red LED. NextBNC

SCART plug SCART plug

A SCART plug (short for Syndicat des Constructeurs d'Appareils Radiorécepteurs et Téléviseurs, French for "Television and Radio Manufacturers' Union") is a 21-pin audio/video cord for connecting video devices (including TVs, videotape and DVD players, and game consoles) to one another. The SCART plug is used for sending analog video and audio signals (in stereo) through a multi-wire cable.

Pins for composite video

Pin number

Function

1

Right Audio Output

2

Right Audio Input

3

Left Audio Output / Mono

4

Audio Ground

5

Blue Ground

6

Left Audio Input / Mono

7

Blue

8

Switch Function

9

Green Ground

10

Data 2

11

Green

12

Data 1

13

Red Ground

14

Data Ground

15

Red

16

Contrôle RVB

17

Composite Video Output Ground

18

Masse Contrôle RVB

19

Video Composite Output

20

Video Composite Input

21

Common Ground

Pins for Y/C video components

Pin number

Function

1

Right Audio Output

2

Right Audio Input

3

Left Audio Output

4

Audio Ground

5

Ground

6

Left Audio Input

7 8

Switch Function

9

Ground

10

Data 2

11 12

Data 1

13

Ground

14

Data Ground

15

Chroma Ground

16 17

Video Ground

18 19

Video Composite Output

20

Luminance Input

21

Common Ground

Last update on Thursday October 16, 2008 02:43:14 PM

BNC connector

NextRJ45

BNC connector

BNC connectors (Bayonet-Neill-Concelman or British Naval Connector) are connectors for coaxial cables. The BNC family is made up of the following elements: • • • •

BNC cable connector: is either soldered or crimped to the end of the cable. BNC T-connector: links a computer's network card to the network cable BNC barrel connector: joins two lengths of coaxial cable, to make a longer cable. BNC terminators: placed at both ends of a bus cable to absorb stray signals. They are grounded. A bus network cannot function without them. It would be out of service.

Last update on Thursday October 16, 2008 02:43:14 PM NextRJ11

RJ45 Plug RJ45 plugs

The RJ45 connector (RJ stands for Registered Jack) is one of the main connectors used with Ethernet network cards, and transmits information over twisted pairs of wires. For this reason, it is sometimes called an Ethernet port:

Last update on Thursday October 16, 2008 02:43:14 PM

RJ11 connector

NextDVI

RJ11 Plug

The RJ11 connector (RJ for Registered Jack) is the most commonly used connector for telephone lines. It is similar to the RJ45 connector, but smaller. When found on a computer, the RJ11 is generally meant for a modem NextHDMI

DVI connector

DVI connector

DVI (Digital Video Interface) connectors, found on some graphics cards, are used for sending video signals digitally to screens with a suitable interface. They bypass the needless and potentially qualityreducing digital-analog conversion process.

The DVI interface, however, is soon to become obsolete, with the release of the HDMI interface. Last update on Thursday October 16, 2008 02:43:14 PM NextRJ45 crossover cable

HDMI Interface HDMI interface

HDMI (High Definition Multimedia Interface) is a digital interface for transferring uncompressed, high-definition multimedia data (audio and video). Some have called it "high-definition SCART." Initiated by a consortium of manufacturers including Hitachi, Matsushita, Philips, Silicon Image, Sony, Thomson and Toshiba, the HDMI interface was standardised in 2002 as version 1.0, then revised in May 2004 (version 1.1) and finally in August 2005 (version 1.2). As time goes by, it will be included little by litle with audio and video equipment, which will carry this logo: The HDMI standard brings with it a new compact connector, compatible with DVI (Digital Video Interface), which looks like this:

Technical characteristics

In terms of capacity, the HDMI interface can reach speeds of about 5 Gbps (HDTV at 2.2Gbps). This can be used to transmit: • •

multichannel sound (up to 8 PCM channels at 24 bits/192 kHz) with a sampling rate of 32 kHz, 44.1kHz, 48kHz or 192kHz; 24-bit high-definition video signals (up to 1920x1080) on three channels (8 bits per channel). The HDMI interface supports all

current video formats and includes three new ones, in order to standardise equipment: o SDTV: 720x480i in NTSC, 720x576i in PAL; o EDTV: 640x480p in VGA, 720x480p in NTSC progressive, 720x576p in PAL progressive; o HDTV: 1280x720p, 1920x1080i Protective measures

The DVI transports a native digital signal between the source and destination devices, which makes it easy to copy the multimedia stream. For this reason, the major film studios and music labels have made data encryption a requirement of the HDMI standard. This mandatory copyright-protection mechanism is named HDCP (High Bandwidth Digital Content Protection). Last update on Thursday October 16, 2008 02:43:14 PM

Creating an RJ45 crossover cable

NextNull-Modem cable

What's an RJ45 plug?

A network card may have several types of connectors, with the most common being: • •

An RJ45 connector; A BNC connector (coaxial cable).

The RJ-45 is the one which interests us here, as it it the most widely used. The cables used are called twisted pairs, as they are made up of four pairs of wires braided together. Each pair of wires is made up of a solid-coloured wire and a wire marked with stripes of that same colour. It is highly recommended to use a category 5 cable between 3 and 90 metres long. There are two wiring standards which differ in the position of the orange and green pairs, defined by the Electronic Industry Association/Telecommunications Industry Association: TIA/EIA 568A TIA/EIA 568B

RJ45 connector on a male plug seen from the front, with contacts pointing up. Connector 1, at left, as seen on a female plug (network card or wall outlet) and at right on a male plug, connector pointing outwards, contacts upwards. Why use a patch cable

RJ45 is normally used to connect computers by way of a hub (a distribution box into which the RJ45 cables coming from the local area network computers are connected) or a switch.

When a computer is connected into a hub or switch, the cable used is called a patch cable, which means that a wire linked to plug 1 on one end is linked to plug 1 on the other end. The standard generally used for making patch cables is TIA/EIA T568A; however, there are also TIA/EIA T568B patch cables (the only difference is the colours of some of the wires, which does not affect the proper functioning of the connection, as long as the wires are joined the same way). Why use a crossover cable

A hub is very useful for connecting many computers, and overall is faster than a coaxial cable connection. Nevertheless, to connect two machines to one another, there is a way to avoid having to use a hub. It involves using a crossover cable (also called a cross cable), which has two wire that cross over one another. The recommended standard for this type of cable is TIA/EIA T568A for one of the ends, and TIA/EIA T568B for the other. This kind of cable can, of course, be purchased, but it is very easy to make on one's own. Making a crossover cable

To make an RJ45 crossover cable, buy a patch cable, split it in the middle, and then reconnect the wires as follows: End 1

End 2

Name #

Colour

Name #

Colour

TD+

1 White/Green RD+

3 White/Orange

TD-

2 Green

6 orange

RD+

3 White/Orange TD+

RD-

1 White/Green

Not used 4 Blue

Not used 4 Blue

Not used 5 White/Blue

Not used 5 White/Blue

RD-

TD-

6 orange

2 Green

Not used 7 White/Brown: Not used 7 White/Brown: Not used 8 Brown

Not used 8 Brown

The ground strap is not crossed, so you don't have to split it.

Linking two PCs with a null modem cable Linking two computers without network cards

The best way to link two computers is to use an RJ45 cable to connect the machines' network cards. However, when one or both of the computers has no network card, there is still a fairly easy way to connect them, by using communication ports (found on every PC). To connect the two computers, you can use a cable called a null modem cable. What's a null modem cable?

A null modem cable is a 6-conductor shielded cable (meaning 6 wires surrounded by a ground strap), with a serial port connector at both ends. It acts as an inverter cable which matches up the data-sending pins and the data-receiving serial ports of both computers. Technically speaking, it used to link two DTEs without going through two DCEs. The resulting connection, however, cannot be longer than 250 metres. To create a null modem cable, then, all that is required is to correctly solder the "correct" wires on both ends of the cable. A PC normally has two kinds of ports:

A 25-pin parallel port called DB25 A 9-pin serial port called DB9

• •

So with these ports free on both computers, there are three possible ways to link them by cable: A DB9-DB9 cable A DB25-DB9 cable A DB25-DB25 cable

• • •

DB9-DB9 null modem cable

DB9 Number 1 DB9 Number 2 Name

#

Name

#

RD

2

TD

3

TD

3

RD

2

DTR

4

DSR+CD 6+1

SG

5

SG

5

DSR+CD 6+1 DTR

4

RS

7

CS

8

CS

8

RS

7

DB9-DB25 null modem cable

DB9

DB25

Name

#

Name

#

RD

2

TD

2

TD

3

RD

3

DTR

4

DSR+CD 6+8

SG

5

SG

7

DSR+CD 6+1 DTR

20

RS

7

CS

5

CS

8

RS

4

DB25-DB25 null modem cable

DB25 Name

DB25 #

Name

#

RD

3

TD

2

TD

2

RD

3

DTR

20 DSR+CD 6+8

SG

7

SG

7

DSR+CD 6+8 DTR

20

RS

4

CS

5

CS

5

RS

4