Computer Hardware

Computer hardware From Wikipedia, the free encyclopedia Jump to: navigation, search Computer hardware is the physical part of a computer, including its digital circuitry, as distinguished from the computer software that executes within the hardware. The hardware of a computer is infrequently changed, in comparison with software and hardware data, which are "soft" in the sense that they are readily created, modified or erased on the computer. Firmware is a special type of software that rarely, if ever, needs to be changed and so is stored on hardware devices such as read-only memory (ROM) where it is not readily changed (and is, therefore, "firm" rather than just "soft"). Most computer hardware is not seen by normal users. It is in embedded systems in automobiles, microwave ovens, electrocardiograph machines, compact disc players, and other devices. Personal computers, the computer hardware familiar to most people, form only a small minority of computers (about 0.2% of all new computers produced in 2003). See Market statistics.

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1 Typical PC hardware o 1.1 Motherboard o 1.2 Power supply o 1.3 Storage controllers o 1.4 Video display controller o 1.5 Removable media devices o 1.6 Internal storage o 1.7 Sound card o 1.8 Networking o 1.9 Other peripherals  1.9.1 Input  1.9.2 Output 2 See also

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3 External links

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[edit] Typical PC hardware

A typical personal computer consists of a case or chassis in a tower shape (desktop) and the following parts:

Internals of typical personal computer.

Inside a Custom Computer.

[edit] Motherboard * Motherboard - It is the "body" or mainframe of the computer, through which all other components interface. •

Central processing unit (CPU) - Performs most of the calculations which enable a computer to function, sometimes referred to as the "brain" of the computer. o Computer fan - Used to lower the temperature of the computer; a fan is almost always attached to the CPU, and the computer case will generally have several fans to maintain a constant airflow. Liquid cooling can also be used to cool a computer, though it focuses more on individual parts rather than the overall temperature inside the chassis.

'* Random Access Memory (RAM)' - Fast-access memory that is cleared when the computer is powered-down. RAM attaches directly to the motherboard, and is used to store programs that are currently running.

Random access memory From Wikipedia, the free encyclopedia (Redirected from Random Access Memory) Jump to: navigation, search "RAM" redirects here. For other uses of the word, see Ram.

Example of writable volatile random access memory: Synchronous Dynamic RAM modules, primarily used as main memory in personal computers, workstations, and servers. Computer memory types Volatile • • •

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DRAM, e.g. DDR SDRAM SRAM Upcoming o Z-RAM o TTRAM Historical o Williams tube o

Delay line memory

Non-volatile •

ROM

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PROM EAROM EPROM EEPROM Flash memory Upcoming o FeRAM o MRAM o CBRAM o PRAM o o o o

SONOS RRAM Racetrack memory NRAM Historical o Drum memory o Magnetic core memory o Plated wire memory o Bubble memory o o o o

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Twistor memory

Random access memory (usually known by its acronym, RAM) is a type of computer data storage. Today it takes the form of integrated circuits that allow the stored data to be accessed in any order, i.e. at random. The word random thus refers to the fact that any piece of data can be returned in a constant time, regardless of its physical location and whether or not it is related to the previous piece of data.[1] This contrasts with storage mechanisms such as tapes, magnetic discs and optical discs, which rely on the physical movement of the recording medium or a reading head. In these devices, the movement takes longer than the data transfer, and the retrieval time varies depending on the physical location of the next item. The word RAM is mostly associated with volatile types of memory (such as DRAM memory modules), where the information is lost after the power is switched off. However, many other types of memory are RAM as well (i.e. Random Access Memory), including most types of ROM and a kind of flash memory called NORFlash. •

The first type of random access memory was the magnetic core memory, developed in 1951, and used in all computers up until the development of the static and dynamic RAM integrated circuits in the late 1960s and early 1970s. Prior to the development of the magnetic core memory, computers used relays or vacuum tubes to perform memory functions. [edit] Types of RAM Modern types of writable RAM generally store a bit of data in either the state of a flip-flop, as in SRAM (static RAM), or as a charge in a capacitor (or transistor gate), as in DRAM (dynamic RAM), EPROM, EEPROM and Flash. Some types have circuitry to detect and/or correct random faults called memory errors in the stored data, using parity bits or error correction codes. RAM of the read-only type, ROM, instead uses a metal mask to permanently enable/disable selected transistors, instead of storing a charge in them.

As both SRAM and DRAM are volatile, other forms of computer storage, such as disks and magnetic tapes, have been used as "permanent" storage in traditional computers. Many newer products instead rely on flash memory to maintain data between sessions of use: examples include PDAs, small music players, mobile phones, synthesizers, advanced calculators, industrial instrumentaion and robotics, and many other types of products; even certain categories of personal computers, such as the OLPC XO-1, Asus Eee PC, and others, have begun replacing magnetic disk with so called flash drives (similar to fast memory cards equipped with an IDE or SATA interface). There are two basic types of flash memory: the NOR type, which is capable of true random access, and the NAND type, which is not; the former is therefore often used in place of ROM, while the latter is used in most memory cards and solid-state drives, due to a lower price. [edit] Memory hierarchy Many computer systems have a memory hierarchy consisting of CPU registers, ondie SRAM caches, external caches, DRAM, paging systems, and virtual memory or swap space on a hard drive. This entire pool of memory may be referred to as "RAM" by many developers, even though the various subsystems can have very different access times, violating the original concept behind the random access term in RAM. Even within a hierarchy level such as DRAM, the specific row, column, bank, rank, channel, or interleave organization of the components make the access time variable, although not to the extent that rotating storage media or a tape is variable. (Generally, the memory hierarchy follows the access time with the fast CPU registers at the top and the slow hard drive at the bottom.) In most modern personal computers, the RAM comes in easily upgraded form of modules called memory modules or DRAM modules about the size of a few sticks of chewing gum. These can quickly be replaced should they become damaged or too small for current purposes. As suggested above, smaller amounts of RAM (mostly SRAM) are also integrated in the CPU and other ICs on the motherboard, as well as in hard-drives, CD-ROMs, and several other parts of the computer system.

Read-only memory From Wikipedia, the free encyclopedia Jump to: navigation, search The notion of read-only data can also refer to file system permissions. Computer memory types Volatile

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DRAM, e.g. DDR SDRAM SRAM Upcoming o Z-RAM o TTRAM Historical o Williams tube Delay line memory

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ROM PROM EAROM EPROM EEPROM Flash memory Upcoming o FeRAM o MRAM o CBRAM o PRAM o SONOS o RRAM o Racetrack memory o NRAM Historical o Drum memory o Magnetic core memory o Plated wire memory o Bubble memory o o o o

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Twistor memory

Read-only memory (usually known by its acronym, ROM) is a class of storage media used in computers and other electronic devices. Because data stored in ROM cannot be modified (at least not very quickly or easily), it is mainly used to distribute firmware (software that is very closely tied to specific hardware, and unlikely to require frequent updates). Modern semiconductor ROM chips are not immediately distinguishable from similar chips like RAM modules, except by the part numbers printed on the package. In its strictest sense, ROM refers only to mask ROM (the oldest type of solid state ROM), which is fabricated with the desired data permanently stored in it, and thus can

never be modified. However, more modern types such as EPROM and flash EEPROM can be erased and re-programmed multiple times; they are still described as "read-only memory" because the reprogramming process is generally infrequent, comparatively slow, and often does not permit random access writes to individual memory locations, which are possible when reading a ROM. Despite the simplicity of mask ROM, economies of scale and field-programmability often make reprogrammable technologies more flexible and inexpensive, so that mask ROM is rarely used in new products as of 2007.

[edit] Swapping If a computer becomes low on RAM during intensive application cycles, the computer can perform an operation know as "swapping". When this occurs, the computer temporarily uses hard drive space as additional memory. Constantly relying on this type of backup memory is called thrashing, which is generally undesirable because it lowers overall system performance. In order to reduce the dependency on swapping, more RAM can be installed. [edit] Other uses of the term Other physical devices with read/write capability can have "RAM" in their names: for example, DVD-RAM. "Random access" is also the name of an indexing method: hence, disk storage is often called "random access" because the reading head can move relatively quickly from one piece of data to another, and does not have to read all the data in between. However the final "M" is crucial: "RAM" (provided there is no additional term as in "DVD-RAM") always refers to a solid-state device.

[edit] RAM disks Software can "partition" a portion of a computer's RAM, allowing it to act as a much faster hard drive that is called a RAM disk. Unless the memory used is nonvolatile, a RAM disk loses the stored data when the computer is shut down. However, volatile memory can retain its data when the computer is shut down if it has a separate power source, usually a battery.

[edit] Recent developments Several new types of non-volatile RAM, which will preserve data while powered down, are under development. The technologies used include carbon nanotubes and the magnetic tunnel effect. In summer 2003, a 128 KB magnetic RAM chip manufactured with 0.18 µm technology was introduced. The core technology of MRAM is based on the magnetic tunnel effect. In June 2004, Infineon Technologies unveiled a 16 MB[2] prototype again based on 0.18 µm technology. Nantero built a functioning carbon nanotube memory prototype 10 GB[2] array in 2004. Whether

some of these technologies will be able to eventually take a significant market share from either DRAM, SRAM, or flash-memory technology, remains to be seen however. In 2006, "Solid-state drives" (based on flash memory) with capacities exceeding 150 gigabytes and speeds far exceeding traditional disks have become available. This development has started to blur the definition between traditional random access memory and "disks", dramatically reducing the difference in performance.

[edit] Memory wall The "memory wall" is the growing disparity of speed between CPU and memory outside the CPU chip. An important reason for this disparity is the limited communication bandwidth beyond chip boundaries. From 1986 to 2000, CPU speed improved at an annual rate of 55% while memory speed only improved at 10%. Given these trends, it was expected that memory latency would become an overwhelming bottleneck in computer performance. [3] Currently, CPU speed improvements have slowed significantly partly due to major physical barriers and partly because current CPU designs have already hit the memory wall in some sense. Intel summarized these causes in their Platform 2015 documentation (PDF): “First of all, as chip geometries shrink and clock frequencies rise, the transistor leakage current increases, leading to excess power consumption and heat (more on power consumption below). Secondly, the advantages of higher clock speeds are in part negated by memory latency, since memory access times have not been able to keep pace with increasing clock frequencies. Third, for certain applications, traditional serial architectures are becoming less efficient as processors get faster (due to the so-called Von Neumann bottleneck), further undercutting any gains that frequency increases might otherwise buy. In addition, partly due to limitations in the means of producing inductance within solid state devices, resistance-capacitance (RC) delays in signal transmission are growing as feature sizes shrink, imposing an additional bottleneck that frequency increases don't address.” The RC delays in signal transmission were also noted in Clock Rate versus IPC: The End of the Road for Conventional Microarchitectures which projects a maximum of 12.5% average annual CPU performance improvement between 2000 and 2014. The data on Intel Processors clearly shows a slowdown in performance improvements in recent processors. However, Intel's new processors, Core 2 Duo (codenamed Conroe) show a significant improvement over previous Pentium 4 processors; due to a more efficient architecture, performance increased while clock rate actually decreased.

[edit] Security concerns

Contrary to simple models (and perhaps common belief), the contents of modern SDRAM modules aren't lost immediately when the computer is shutdown; instead, the contents fade away - a process that takes only seconds at room temperatures, but which can be extended to minutes at low temperatures. As an example, it is therefore possible to get hold of an encryption key if it was stored in ordinary working memory (i.e. the SDRAM modules).[4]

* Firmware is loaded from the Read only memory ROM run from the Basic InputOutput System (BIOS) or in newer systems Extensible Firmware Interface (EFI) compliant •

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Internal Buses - Connections to various internal components. o PCI o PCI-E o USB o HyperTransport o CSI (expected in 2008) o AGP (being phased out) o VLB (outdated) External Bus Controllers - used to connect to external peripherals, such as printers and input devices. These ports may also be based upon expansion cards, attached to the internal buses. o parallel port o serial port o USB o firewire o SCSI (On Servers and older machines) o PS/2 (For mice and keyboards, being phased out and replaced by USB.) o ISA (outdated) o EISA (outdated) o MCA (outdated)

[edit] Power supply Main article: Computer power supply A case control, and (usually) a cooling fan, and supplies power to run the rest of the computer, the most common types of power supplies are AT and BabyAT (old) but the standard for PCs actually are ATX and Micro ATX.

[edit] Storage controllers

Controllers for hard disk, CD-ROM and other drives like internal Zip and Jaz conventionally for a PC are IDE/ATA; the controllers sit directly on the motherboard (on-board) or on expansion cards, such as a Disk array controller. IDE is usually integrated, unlike SCSISmall Computer System Interface which is found in most servers. The floppy drive interface is a legacy MFM interface which is now slowly disappearing. All these interfaces are gradually being phased out to be replaced by SATA and SAS.

[edit] Video display controller Main article: Graphics card Produces the output for the visual display unit. This will either be built into the motherboard or attached in its own separate slot (PCI, PCI-E, PCI-E 2.0, or AGP), in the form of a Graphics Card.

[edit] Removable media devices Main article: Computer storage •

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CD (compact disc) - the most common type of removable media, inexpensive but has a short life-span. o CD-ROM Drive - a device used for reading data from a CD. o CD Writer - a device used for both reading and writing data to and from a CD. DVD (digital versatile disc) - a popular type of removable media that is the same dimensions as a CD but stores up to 6 times as much information. It is the most common way of transferring digital video. o DVD-ROM Drive - a device used for reading data from a DVD. o DVD Writer - a device used for both reading and writing data to and from a DVD. o DVD-RAM Drive - a device used for rapid writing and reading of data from a special type of DVD. Blu-ray - a high-density optical disc format for the storage of digital information, including high-definition video. o BD-ROM Drive - a device used for reading data from a Blu-ray disc. o BD Writer - a device used for both reading and writing data to and from a Blu-ray disc. HD DVD - a high-density optical disc format and successor to the standard DVD. It was a discontinued competitor to the Blu-ray format. Floppy disk - an outdated storage device consisting of a thin disk of a flexible magnetic storage medium. Zip drive - an outdated medium-capacity removable disk storage system, first introduced by Iomega in 1994. USB flash drive - a flash memory data storage device integrated with a USB interface, typically small, lightweight, removable, and rewritable.

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Tape drive - a device that reads and writes data on a magnetic tape, usually used for long term storage.

[edit] Internal storage Hardware that keeps data inside the computer for later use and remains persistent even when the computer has no power. • • •

Hard disk - for medium-term storage of data. Solid-state drive - a device similar to hard disk, but containing no moving parts. Disk array controller - a device to manage several hard disks, to achieve performance or reliability improvement.

[edit] Sound card Main article: Sound card Enables the computer to output sound to audio devices, as well as accept input from a microphone. Most modern computers have sound cards built-in to the motherboard, though it is common for a user to install a separate sound card as an upgrade.

[edit] Networking Main article: Computer networks Connects the computer to the Internet and/or other computers. • • •

Modem - for dial-up connections Network card - for DSL/Cable internet, and/or connecting to other computers. Direct Cable Connection - Use of a null modem, connecting two computers together using their serial ports or a Laplink Cable, connecting two computers together with their parallel ports.

dial up connections broad band connections

[edit] Other peripherals Main article: Peripheral In addition, hardware devices can include external components of a computer system. The following are either standard or very common.

Wheel mouse Includes various input and output devices, usually external to the computer system [edit] Input Main article: Input •

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Text input devices o Keyboard - a device, to input text and characters by depressing buttons (referred to as keys), similar to a typewriter. The most common English-language key layout is the QWERTY layout. Pointing devices o Mouse - a pointing device that detects two dimensional motion relative to its supporting surface. o Trackball - a pointing device consisting of an exposed portruding ball housed in a socket that detects rotation about two axes. o Xbox 360 Controller - A controller used for Xbox 360, Which with the use of the application Switchblade(tm), can be used as an additional pointing device with the left or right thumbstick. Gaming devices o Joystick - a general control device that consists of a handheld stick that pivots around one end, to detect angles in two or three dimensions. o Gamepad - a general game controller held in the hand that relies on the digits (especially thumbs) to provide input. o Game controller - a specific type of controller specialized for certain gaming purposes. Image, Video input devices o Image scanner - a device that provides input by analyzing images, printed text, handwriting, or an object. o Webcam - a low resolution video camera used to provide visual input that can be easily transferred over the internet. Audio input devices o Microphone - an acoustic sensor that provides input by converting sound into an electrical signals

[edit] Output Main article: Output •

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Image, Video output devices o Printer o Monitor Audio output devices o Speakers o Headset