Hardware Notes

Main parts Motherboard Microprocessor ( processor ) Hard disk drive ( HDD) RAM Display card Cdrom drive Floppy disk drive ( FDD) Modem Ports Printers Keyboard Mouse

Motherboard

Modern Pentium class motherboards have a data bus with 64 bitsThat is the width of the data highway that goes in and out of the processor. The Pentium processors, however, do use 32-bit registers to handle 32-bit instructions. Bus speeds and widths have increased due to faster processors and the needs of multimedia applications. Typical bus names and widths are: • • • • • •

Industry Standard Architecture (ISA) - 8 or 16 bits Extended Industry Standard Architecture (EISA) - 8 or16 bits Microchannel Architecture (MCA) - 16 or 32 bits VESA Local Bus (VLB) - 32 bits Peripheral Component Interconnect (PCI) - 32 or 64 bits Accelerated Graphics Port (AGP ) - 32 bits

Chipsets provide the support for the processor chip on the motherboard. The Intel 440BX is the dominant chipset in the non-Apple pc’s. The chipset is the heart of the computer since it controls and determines how fast and which type of processor, memory, and slots are used. Another chip on the motherboard is called the Super I/O controller. Its main function is to control the fdd, kbd, mouse , serialand printer ports. Check out PCGuide's super i/o controller funtionsto learn more. Recent motherboard designs include additional chips to support USB, sound card, video adapter, computer host and network adapter. These chips save the cost of an adapter slot.

Market availabilities are a mojor concern for any hardware assembler . we have to be very careful in choosing the harware required , available and compatibility. Motherboards available are of 2 types 1) Originals :These are the one’s that have been originally made for the specified proscessors and are manufactured for the companies itself . 2) Chipsets :These are the cheaper substitutes which are easily available and are give reasonably good performance .

1) Check if the motherboard is of the specified type and matches the dimensions of the cabinet being used ( ie. Mini tower, micro atx, atx ) 2) See the instructions provided in the manul about the powersupply requirements, etc… 3) Check the no. of screws and clips required with the one’s available . 4) Place the motherboard in the cabinet base and fix it with the screws provided. 5) Take care to see if u have no contact between the motherboard and the cabinet base, apart from the screws and clips. 6) Connect the necessary powersupply chords and the port interfaces .

Microprocessor ( processor )

A microprocessor -- also known as a CPU or central processing unit -- is a complete computation engine that is fabricated on a single chip. The first microprocessor was the Intel 4004, introduced in 1971. The 4004 was not very powerful -- all it could do was add and subtract, and it could only do that 4 bits at a time. But it was amazing that everything was on one chip. 4004 powered one of the first portable electronic calculators. The first microprocessor to make it into a home computer was the Intel 8080, a complete 8-bit computer on one chip, introduced in 1974. The first microprocessor to make a real splash in the market was the Intel 8088, introduced in 1979 and incorporated into the IBM PC (which first appeared around 1982). If you are familiar with the PC market and its history, you know that the PC market moved from the 8088 to the 80286 to the 80386 to the 80486 to the Pentium to the Pentium II to the Pentium III to the Pentium 4. All of these microprocessors are made by Intel and all of them are improvements on the basic design of the 8088. The Pentium 4 can execute any piece of code that ran on the original 8088, but it does it about 5,000 times faster! The following table helps you to understand the differences between the different processors that Intel has introduced over the years. Name

Date Transistors Microns

Clock speed

Data width

MIPS

80286

1982

134,000

1.5

6 MHz

16 bits

1

80386

1985

275,000

1.5

16 MHz

32 bits

5

80486

1989

1,200,000

1

25 MHz

32 bits

20

Pentium 1993

3,100,000

0.8

60 MHz

32 bits 64-bit bus

100

Pentium 1997 II

7,500,000

0.35

233 MHz

32 bits 64-bit bus

~300

Pentium 1999 III

9,500,000

0.25

450 MHz

32 bits 64-bit bus

~510

Pentium 2000 42,000,000 4

0.18

1.5 GHz

32 bits ~1,700 6 4-bit bus

Prcessors as we call them , are available in two basic types 1) Slot type :slot type are the one’s that hav a fan attached to it and r inserted like a video game cartridge in the slot provided. 2) copper mine ( flat pack ) :these are available in a flat type construction and are having a no. of connecting pins all around them .

1) check the type of processor available and it’s provisions for it on the motherboard . 2) check if the heat sink available is suitable and the fan provided is working perfectly. 3) Fit the fan on the processor and place the heat sink in it’s required position and connect the suppy to the fan. 4) Place the processor on the motherboard and fix it

Hard disk drive ( HDD)

Usually, these devices connect to the computer through an Integrated Drive Electronics (IDE) interface. Essentially, an IDE interface is a standard way for a storage device to connect to a computer. IDE is actually not the true technical name for the interface standard. The original name, AT Attachment (ATA), signified that the interface was initially developed for the IBM AT computer. You will learn about the evolution of IDE/ATA, what the pinouts are and exactly what "slave" and "master" mean in IDE.

Cable Key IDE devices use a ribbon cable to connect to each other. Ribbon cables have all of the wires laid flat next to each other instead of bunched or wrapped together in a bundle. IDE ribbon cables have either 40 or 80 wires. There is a connector at each end of the cable and another one about two-thirds of the distance from the motherboard connector. This cable cannot exceed 18 inches (46 cm) in total length (12 inches from first to second connector, and 6 inches from second to third) to maintain signal integrity. The three connectors are typically different colors and attach to specific items: • • •

The blue connector attaches to the motherboard. The black connector attaches to the primary (master) drive. The grey connector attaches to the secondary (slave) drive.

Along one side of the cable is a stripe. This stripe tells you that the wire on that side is attached to Pin 1 of each connector. Wire 20 is not connected to anything.

In fact, there is no pin at that position. This position is used to ensure that the cable is attached to the drive in the correct position. Another way that manufacturers make sure the cable is not reversed is by using a cable key. The cable key is a small, plastic square on top of the connector on the ribbon cable that fits into a notch on the connector of the device. This allows the cable to attach in only one position.

pin Description Pin Description Reset -IOW 1 23 Ground Ground 2 24 Data Bit 7 -IOR 3 25 Data Bit 8 Ground 4 26 Data Bit 6 I/O Channel Ready 5 27 Data Bit 9 SPSYNC: Cable Select 6 28 Data Bit 5 -DACK 3 7 29 Data Bit 10 Ground 8 30 Data Bit 4 RQ 14 9 31 Data Bit 11 -IOCS 16 10 32 Data Bit 3 Address Bit 1 11 33 Data Bit 12 -PDIAG 12 34 Data Bit 2 Address Bit 0 13 35 Data Bit 13 Address Bit 2 14 36 Data Bit 1 -CS1FX 15 37 Data Bit 14 -CS3FX 16 38 Data Bit 0 -DA/SP 17 39 Data Bit 15 Ground 18 40 Ground +5 Volts (Logic) (Optional) 19 41 20 Cable Key (pin missing) 42 +5 Volts (Motor) (Optional) DRQ 3 Ground (Optional) 21 43 Ground -Type (Optional) 22 44

Note that the last four pins are only used by devices that require power through the ribbon cable. Typically, such devices are hard drives that are too small (for example, 2.5 inches) to need a separate power supply.

A single IDE interface can support two devices. Most motherboards come with dual IDE interfaces (primary and secondary) for up to four IDE devices. Because the controller is integrated with the drive, there is no overall controller to decide which device is currently communicating with the computer. This is not a problem as long as each device is on a separate interface, but adding support for a second drive on the same cable took some ingenuity. To allow for two drives on the same cable, IDE uses a special configuration called master and slave. This configuration allows one drive's controller to tell the other drive when it can transfer data to or from the computer. What happens is the slave drive makes a request to the master drive, which checks to see if it is currently communicating with the computer. If the master drive is idle, it tells the slave drive to go ahead. If the master drive is communicating with the computer, it tells the slave drive to wait and then informs it when it can go ahead. The computer determines if there is a second (slave) drive attached through the use of Pin 39 on the connector. Pin 39 carries a special signal, called Drive Active/Slave Present (DASP), that checks to see if a slave drive is present. Although it will work in either position, it is recommended that the master drive is attached to the connector at the very end of the IDE ribbon cable. Then, a jumper on the back of the drive next to the IDE connector must be set in the correct position to identify the drive as the master drive. The slave drive must have either the master jumper removed or a special slave jumper set, depending on the drive. Also, the slave drive is attached to the connector near the middle of the IDE ribbon cable. Each drive's controller board looks at the jumper setting to determine whether it is a slave or a master. This tells them how to perform. Every drive is capable of being either slave or master when you receive it from the manufacturer. If only one drive is installed, it should always be the master drive. Many drives feature an option called Cable Select (CS). With the correct type of IDE ribbon cable, these drives can be auto configured as master or slave. CS works like this: A jumper on each drive is set to the CS option. The cable itself is just like a normal IDE cable except for one difference -- Pin 28 only connects to the master drive connector. When your computer is powered up, the IDE interface sends a signal along the wire for Pin 28. Only the drive attached to the master connector receives the signal. That drive then configures itself as the master drive. Since the other drive received no signal, it defaults to slave mode.

In the market there r mainly ordinary hdd’s available which r running at a 7200 rpm . We hav also some special hdd’s available which are of the type SCSI , needin a special interface card ( scsi card ) which allows twice or even mor the speed than normal

1) check for a required place to keep the hdd] 2) check if there is a required cable and ide slot for the hdd connection 3) make the necessary jumper settings in order to hav a proper working of the hard disk 4) connect the hdd only when powersupply is off .

RAM

Random access memory (RAM) is the best known form of computer memory. RAM is considered "random access" because you can access any memory cell directly if you know the row and column that intersect at that cell. The opposite of RAM is serial access memory (SAM). SAM stores data as a series of memory cells that can only be accessed sequentially (like a cassette tape). If the data is not in the current location, each memory cell is checked until the needed data is found. SAM works very well for memory buffers, where the data is normally stored in the order in which it will be used (a good example is the texture buffer memory on a video card). RAM data, on the other hand, can be accessed in any order. Memory chips are normally only available as part of a card called a module. You've probably seen memory listed as 8x32 or 4x16. These numbers represent the number of the chips multiplied by the capacity of each individual chip, which is measured in megabits (Mb), or one million bits. Take the result and divide it by eight to get the number of megabytes on that module. For example, 4x32 means that the module has four 32-megabit chips. Multiply 4 by 32 and you get 128 megabits. Since we know that a byte has 8 bits, we need to divide our result of 128 by 8. Our result is 16 megabytes! The type of board and connector used for RAM in desktop computers has evolved over the past few years. The first types were proprietary, meaning that different computer manufacturers developed memory boards that would only work with their specific systems. Then came SIMM, which stands for single inline memory module. This memory board used a 30-pin connector and was about 3.5 inches by .75 inches (about 9 centimeters by 2 centimeters) in size. In most computers, you had to install SIMMs in pairs of equal capacity and speed. This is because the width of the bus is more than a single SIMM. For example, you would install two 8-megabyte (MB) SIMMs to get 16 megabytes total RAM. Each SIMM could send 8 bits of data at one time while the system bus could

handle 16 bits at a time. Later SIMM boards, slightly larger at 4.25 inches by 1 inch (about 11 centimeters by 2.5 centimeters), used a 72-pin connector for increased bandwidth and allowed for up to 256 MB of RAM. As processors grew in speed and bandwidth capability, the industry adopted a new standard in dual in-line memory module (DIMM). With a whopping 168-pin connector and a size of 5.4 inches by 1 inch (about 14 centimeters by 2.5 centimeters), DIMMs range in capacity from 8 MB to 128 MB per module and can be installed singly instead of in pairs. Most PC memory modules operate at 3.3 volts, while Mac systems typically use 5 volts. A new standard, Rambus in-line memory module (RIMM), is comparable in size and pin configuration to DIMM but uses a special memory bus to greatly increase speed. Many brands of notebook computers use proprietary memory modules, but several manufacturers use RAM based on the small outline dual in-line memory module (SODIMM) configuration. SODIMM cards are small, about 2 inches by 1 inch (5 centimeters by 2.5 centimeters), and have 144 pins. Capacity ranges from 16 MB to 256 MB per module. An interesting fact about the Apple iMac desktop computer is that it uses SODIMMs instead of the traditional DIMMs.

Static random access memory uses multiple transistors, typically four to six, for

each memory cell but doesn't have a capacitor in each cell. It is used primarily for cache Dynamic random access memory has memory cells with a paired transistor and capacitor requiring constant refreshing. Fast page mode dynamic random access memory was the original form of DRAM. It waits through the entire process of locating a bit of data by column and row and then reading the bit before it starts on the next bit. Maximum transfer rate to L2 cache is approximately 176 megabytes per second. ! "

Extended data-out dynamic random access memory does not wait for all of the processing of the first bit before continuing to the next one. As soon as the address of the first bit is located, EDO DRAM begins looking for the next bit. It is about five percent faster than FPM. Maximum transfer rate to L2 cache is approximately 264 megabytes per second. Synchronous dynamic random access memory takes advantage of the burst mode concept to greatly improve performance. It does this by staying on the row containing the requested bit and moving rapidly through the columns, reading each bit as it goes. The idea is that most of the time the data needed by the CPU will be in sequence. SDRAM is about five percent faster than EDO RAM and is the most common form in desktops today. Maximum transfer rate to L2 cache is approximately 528 megabytes per second. Rambus dynamic random access memory is a radical departure from the previous DRAM architecture. Designed by Rambus, RDRAM uses a Rambus inline memory module (RIMM), which is similar in size and pin configuration to a standard DIMM. What makes RDRAM so different is its use of a special highspeed data bus called the Rambus channel. RDRAM memory chips work in parallel to achieve a data rate of 800 MHz. #

Another self-contained DRAM module for notebooks, cards of this type are not proprietary and should work with any notebook computer whose system bus matches the memory card's configuration. In the previous section, we discussed how much RAM is needed in most situations. RAM is usually sold in multiples of 16 megabytes: 16, 32, 64, 128 and 256. This means that if you currently have a system with 64-MB RAM and you want at least 100-MB RAM total, then you will probably need to add another 64MB module.

In the market there are various types of makes of RAM’s available but the most simple one’s are 1) Edo Ram. 2) Sd Ram 3) Rd Ram

1) Check if u hav the required RAM according to the patters and connectors shown above 2) Clean the RAM slots in the motherboard. 3) Place the RAM in the slot and , pres hard till it is fitted tightly into the slot.

Display cards

You will learn about AGP, or Accelerated Graphics Port. AGP was developed by Intel as a way to enhance the performance and speed of the graphics hardware connected to a PC. You will learn how AGP came about, how it works and what the future holds for PC graphics subsystems. You may always wonder why need DISPLAY cards ! well this is to answer your questions ina very simplified and easy way . We need to see wht work we do on the Pc , that can be done only on our monitor and we provide the necessay diplay on it . Thus we need th pc to generate out diplay which is done by our display card .

They are of different types and configurations 1) Onboard display cards :These are the display cards which are readily available on the motherboard itself. 2) External :These have to be externally put on to the AGP slot provided in the motherboard.

1) check if ther is a display card already provided on the motherboard , by reading the manual 2) if yes , try installing it

3) if no , place the display card in th AGP slot and install it.

Cd rom Drive

Floppy disk drive ( FDD)

The major parts of a FDD include: •

•

•

•

•

Read/Write Heads: Located on both sides of a diskette, they move together on the same assembly. The heads are not directly opposite each other in an effort to prevent interaction between write operations on each of the two media surfaces. The same head is used for reading and writing, while a second, wider head is used for erasing a track just prior to it being written. This allows the data to be written on a wider "clean slate," without interfering with the analog data on an adjacent track. Drive Motor: A very small spindle motor engages the metal hub at the center of the diskette, spinning it at either 300 or 360 rotations per minute (RPM). Stepper Motor: This motor makes a precise number of stepped revolutions to move the read/write head assembly to the proper track position. The read/write head assembly is fastened to the stepper motor shaft. Mechanical Frame: A system of levers that opens the little protective window on the diskette to allow the read/write heads to touch the dualsided diskette media. An external button allows the diskette to be ejected, at which point the spring-loaded protective window on the diskette closes. Circuit Board: Contains all of the electronics to handle the data read from or written to the diskette. It also controls the stepper-motor control circuits used to move the read/write heads to each track, as well as the movement of the read/write heads toward the diskette surface.

The read/write heads do not touch the diskette media when the heads are traveling between tracks. Electronic optics check for the presence of an opening in the lower corner of a 3.5-inch diskette (or a notch in the side of a 5.25-inch diskette) to see if the user wants to prevent data from being written on it.

There are basically 2 main types of floppy disk drives available in the markets which are specific to the types of floppies being used 1) 3 ½ “ floppy drive 2) 5 ¼ “ floppy drive

1) check the floppy disk available to u and accordingly choose the floppy disk connector for data cable and power supply. 2) Place the floppy drive in the cabinet and fix it

Modem

external modem

internal modem

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The word "modem" is a contraction of the words modulator-demodulator. A modem is typically used to send digital dataover aphone line.

The sending modem modulates the data into a signal that is compatible with the phone line, and the receiving modem demodulates the signal back into digital data. Wireless modems convert digital data into radio signals and back. Modems came into existence in the 1960s as a way to allow terminals to connect to computers over the phone lines. A typical arrangement is shown below:

In a configuration like this, a dumb terminal at an off-site office or store could "dial in" to a large, central computer. The 1960s were the age of time-shared computers, so a business would often buy computer time from a time-share facility and connect to it via a 300-bit-per-second (bps) modem. A dumb terminal is simply a keyboard and a screen. A very common dumb terminal at the time was called the DEC VT-100, and it became a standard of the day (now memorialized in terminal emulators worldwide). The VT-100 could display 25 lines of 80 characters each. When the user typed a character on the terminal, the modem sent the ASCII code for the character to the computer. The computer then sent the character back to the computer so it would appear on the screen. When personal computers started appearing in the late 1970s, bulletin board systems (BBS) became the rage. A person would set up a computer with a modem or two and some BBS software, and other people would dial in to connect to the bulletin board. The users would run terminal emulators on their computers to emulate a dumb terminal. People got along at 300 bps for quite a while. The reason this speed was tolerable was because 300 bps represents about 30 characters per second, which is a lot more characters per second than a person can type or read. Once people started transferring large programs and images to and from bulletin board systems, however, 300 bps became intolerable. Modem speeds went through a series of steps at approximately two-year intervals: • • • • • •

300 bps - 1960s through 1983 or so 1200 bps - Gained popularity in 1984 and 1985 2400 bps 9600 bps - First appeared in late 1990 and early 1991 19.2 kilobits per second (Kbps) 28.8 Kbps

• • •

33.6 Kbps 56 Kbps - Became the standard in 1998 ADSL, with theoretical maximum of up to 8 megabits per second (Mbps) Gained popularity in 1999

Ports

If you have a printer connected to your computer, there is a good chance that it uses the parallel port. While USB is becoming increasingly popular, the parallel port is still a commonly used interface for printers.

There are various types of ports available in our computer

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Just about any computer that you buy today comes with one or more Universal Serial Bus connectors on the back. These USB connectors let you attach everything from mice to printers to your computer quickly and easily. The operating system supports USB as well, so the installation of the device drivers is quick and easy, too. Compared to other ways of connecting devices to your computer (including parallell, serial and special cards that you install inside the computer's case), USB devices are incredibly simple

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usb connector

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Parallel ports were originally developed by IBM as a way to connect a printer to your PC. When IBM was in the process of designing the PC, the company wanted the computer to work with printers offered by Centronics, a top printer

manufacturer at the time. IBM decided not to use the same port interface on the computer that Centronics used on the printer.

Instead, IBM engineers coupled a 25-pin connector, DB-25, with a 36-pin Centronics connector to create a special cable to connect the printer to the computer. Other printer manufacturers ended up adopting the Centronics interface, making this strange hybrid cable an unlikely de facto standard. When a PC sends data to a printer or other device using a parallel port, it sends 8 bits of data (1 byte) at a time. These 8 bits are transmitted parallel to each other, as opposed to the same eight bits being transmitted serially (all in a single row) through a serial port. The standard parallel port is capable of sending 50 to 100 kilobytes of data per second. Let's take a closer look at what each pin does when used with a printer: •

•

•

• • •

• •

Pin 1 carries the strobe signal. It maintains a level of between 2.8 and 5 volts, but drops below 0.5 volts whenever the computer sends a byte of data. This drop in voltage tells the printer that data is being sent. Pins 2 through 9 are used to carry data. To indicate that a bit has a value of 1, a charge of 5 volts is sent through the correct pin. No charge on a pin indicates a value of 0. This is a simple but highly effective way to transmit digital information over an analog cable in real-time. Pin 10 sends the acknowledge signal from the printer to the computer. Like Pin 1, it maintains a charge and drops the voltage below 0.5 volts to let the computer know that the data was received. If the printer is busy, it will charge Pin 11. Then, it will drop the voltage below 0.5 volts to let the computer know it is ready to receive more data. The printer lets the computer know if it is out of paper by sending a charge on Pin 12. As long as the computer is receiving a charge on Pin 13, it knows that the device is online. The computer sends an auto feed signal to the printer through Pin 14 using a 5-volt charge. If the printer has any problems, it drops the voltage to less than 0.5 volts on Pin 15 to let the computer know that there is an error. Whenever a new print job is ready, the computer drops the charge on Pin 16 to initialize the printer.

•

•

Pin 17 is used by the computer to remotely take the printer offline. This is accomplished by sending a charge to the printer and maintaining it as long as you want the printer offline. Pins 18-25 are grounds and are used as a reference signal for the low (below 0.5 volts) charge.

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These are the most versatile and most commonly used ports available in all kinds of systems. They are basically used to connect modems, mice, etc….

Printers

Printers are a very important peripheral device used in our day to day life and probably the most simplest of out hardware . They are used to obtain hardcopies of our created files , etc…

They are of various types 1) Dot matrix : 2) Deskjet 3) Laser printer

1) Check the type of printer being used. 2) Connect the powersupply chord to the mains. 3) Connect the printer data cable to the printer port ( Lpt).

Keyboard

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Keyboards have changed very little in layout since their introduction. In fact, the most common change has simply been the natural evolution of adding more keys that provide additional functionality. The most common keyboards are: • • • •

101-key Enhanced keyboard 104-key Windows keyboard 82-key Apple standard keyboard 108-key Apple Extended keyboard

Portable computers such as laptops quite often have custom keyboards that have slightly different key arrangements than a standard keyboard. Also, many system manufacturers add specialty buttons to the standard layout. A typical keyboard has four basic types of keys: • • • •

Typing keys Numeric keypad Function keys Control keys

The typing keys are the section of the keyboard that contain the letter keys, generally laid out in the same style that was common for typewriters. This layout, known as QWERTY for the first six letters in the layout, was originally designed to slow down fast typists by making the arrangement of the keys somewhat awkward! The reason that typewriter manufacturers did this was because the mechanical arms that imprinted each character on the paper could jam together if the keys were pressed too rapidly. Because it has been long established as a standard, and people have become accustomed to the QWERTY configuration, manufacturers developed keyboards for computers using the same layout, even though jamming is no longer an issue. Critics of the QWERTY layout have adopted another layout, Dvorak, that places the most commonly used letters in the

most convenient arrangementThe numeric keypad is a part of the natural evolution mentioned previously. As the use of computers in business environments increased, so did the need for speedy data entry. Since a large part of the data was numbers, a set of 17 keys was added to the keyboard. These keys are laid out in the same configuration used by most adding machines and calculators, to facilitate the transition to computer for clerks accustomed to these other machines. In 1986, IBM extended the basic keyboard with the addition of function and control keys. The function keys, arranged in a line across the top of the keyboard, could be assigned specific commands by the current application or the operating system. Control keys provided cursor and screen control. Four keys arranged in an inverted T formation between the typing keys and numeric keypad allow the user to move the cursor on the display in small increments. The control keys allow the user to make large jumps in most applications. Common control keys include: • • • • • • • • •

Home End Insert Delete Page Up Page Down Control (Ctrl) Alternate (Alt) Escape (Esc)

Mouse

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Most mice in use today use the standard PS/2 type connector, as shown hereThese pins have the following functions (refer to the above photo for pin numbering):

A typical PS/2 connector: Assume that pin 1 is located just to the left of the black alignment pin, and the others are numbered clockwise from there.

1. 2. 3. 4. 5. 6.

Unused +5 volts (to power the chip and LEDs) Unused Clock Ground Data

Whenever the mouse moves or the user clicks a button, the mouse sends 3 bytes of data to the computer. The first byte's 8 bits contain: 1. 2. 3. 4.

Left button state (0 = off, 1 = on) Right button state (0 = off, 1 = on) 0 1

5. X direction (positive or negative) 6. Y direction 7. X overflow (the mouse moved more than 255 pulses in 1/40th of a second) 8. Y overflow The next 2 bytes contain the X and Y movement values, respectively. These 2 bytes contain the number of pulses that have been detected in the X and Y direction since the last packet was sent. The data is sent from the mouse to the computer serially on the data line, with the clock line pulsing to tell the computer where each bit starts and stops. Eleven bits are sent for each byte (1 start bit, 8 data bits, 1 parity bit and 1 stop bit). The PS/2 mouse sends on the order of 1,200 bits per second. That allows it to report mouse position to the computer at a maximum rate of about 40 reports per second. If you are moving the mouse very rapidly, the mouse may travel an inch or more in one-fortieth of a second. This is why there is a byte allocated for X and Y motion in the data protocol.

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There is nothing more upsetting for a PC user than when there is a problem with their machine. This upset can turn quickly to frustration when the problem seems to be impossible to solve, or even to understand. Every PC user has experienced these feelings, but it is in most cases possible to both diagnose and correct most problems with the typical PC. And with some help, you can usually do it yourself. The most important resource you can have at your disposal when you are trying to troubleshoot a problem with your PC is: experience. Those who have done a lot of work diagnosing and correcting problems with a wide variety of PCs develop a knack for recognizing problem situations that they have seen before. They also learn (and invent) techniques that make it possible for them to get to the root of a problem quickly. There's no substitute for experience, but I'm hoping that this Guide will be the next best thing. I have accumulated here the experience of myself and many other knowledgeable PC users, upgraders and maintainers, to help you learn how to detect and correct many common problems that plague PC users. This includes both general rules of thumb regarding how to troubleshoot your PC, as well as information on dealing with vendor warranties, and repairing your machine.