How computers work

Main articles: Central processing unit and Microprocessor

A general purpose computer has four main sections: the arithmetic and logic unit (ALU), the control unit, the memory, and the input and output devices (collectively termed I/O). These parts are interconnected by busses, often made of groups of wires.

The control unit, ALU, registers, and basic I/O (and often other hardware closely linked with these) are collectively known as a central processing unit (CPU). Early CPUs were composed of many separate components but since the mid-1970s CPUs have typically been constructed on a single integrated circuit called a microprocessor.

Control unit
Main articles: CPU design and Control unit

The control unit (often called a control system or central controller) directs the various components of a computer. It reads and interprets (decodes) instructions in the program one by one. The control system decodes each instruction and turns it into a series of control signals that operate the other parts of the computer.[16] Control systems in advanced computers may change the order of some instructions so as to improve performance.

A key component common to all CPUs is the program counter, a special memory cell (a register) that keeps track of which location in memory the next instruction is to be read from.[17]
Diagram showing how a particular MIPS architecture instruction would be decoded by the control system.

The control system's function is as follows—note that this is a simplified description, and some of these steps may be performed concurrently or in a different order depending on the type of CPU:



1. Read the code for the next instruction from the cell indicated by the program counter.
2. Decode the numerical code for the instruction into a set of commands or signals for each of the other systems.
3. Increment the program counter so it points to the next instruction.
4. Read whatever data the instruction requires from cells in memory (or perhaps from an input device). The location of this required data is typically stored within the instruction code.
5. Provide the necessary data to an ALU or register.
6. If the instruction requires an ALU or specialized hardware to complete, instruct the hardware to perform the requested operation.
7. Write the result from the ALU back to a memory location or to a register or perhaps an output device.
8. Jump back to step (1).

Since the program counter is (conceptually) just another set of memory cells, it can be changed by calculations done in the ALU. Adding 100 to the program counter would cause the next instruction to be read from a place 100 locations further down the program. Instructions that modify the program counter are often known as "jumps" and allow for loops (instructions that are repeated by the computer) and often conditional instruction execution (both examples of control flow).

It is noticeable that the sequence of operations that the control unit goes through to process an instruction is in itself like a short computer program—and indeed, in some more complex CPU designs, there is another yet smaller computer called a microsequencer that runs a microcode program that causes all of these events to happen.

Arithmetic/logic unit (ALU)
Main article: Arithmetic logic unit

The ALU is capable of performing two classes of operations: arithmetic and logic.[18]

The set of arithmetic operations that a particular ALU supports may be limited to adding and subtracting or might include multiplying or dividing, trigonometry functions (sine, cosine, etc) and square roots. Some can only operate on whole numbers (integers) whilst others use floating point to represent real numbers—albeit with limited precision. However, any computer that is capable of performing just the simplest operations can be programmed to break down the more complex operations into simple steps that it can perform. Therefore, any computer can be programmed to perform any arithmetic operation—although it will take more time to do so if its ALU does not directly support the operation. An ALU may also compare numbers and return boolean truth values (true or false) depending on whether one is equal to, greater than or less than the other ("is 64 greater than 65?").

Logic operations involve Boolean logic: AND, OR, XOR and NOT. These can be useful both for creating complicated conditional statements and processing boolean logic.

Superscalar computers may contain multiple ALUs so that they can process several instructions at the same time.[19] Graphics processors and computers with SIMD and MIMD features often provide ALUs that can perform arithmetic on vectors and matrices.

Memory
Main article: Computer storage
Magnetic core memory was popular main memory for computers through the 1960s until it was completely replaced by semiconductor memory.

A computer's memory can be viewed as a list of cells into which numbers can be placed or read. Each cell has a numbered "address" and can store a single number. The computer can be instructed to "put the number 123 into the cell numbered 1357" or to "add the number that is in cell 1357 to the number that is in cell 2468 and put the answer into cell 1595". The information stored in memory may represent practically anything. Letters, numbers, even computer instructions can be placed into memory with equal ease. Since the CPU does not differentiate between different types of information, it is up to the software to give significance to what the memory sees as nothing but a series of numbers.

In almost all modern computers, each memory cell is set up to store binary numbers in groups of eight bits (called a byte). Each byte is able to represent 256 different numbers; either from 0 to 255 or -128 to +127. To store larger numbers, several consecutive bytes may be used (typically, two, four or eight). When negative numbers are required, they are usually stored in two's complement notation. Other arrangements are possible, but are usually not seen outside of specialized applications or historical contexts. A computer can store any kind of information in memory as long as it can be somehow represented in numerical form. Modern computers have billions or even trillions of bytes of memory.

The CPU contains a special set of memory cells called registers that can be read and written to much more rapidly than the main memory area. There are typically between two and one hundred registers depending on the type of CPU. Registers are used for the most frequently needed data items to avoid having to access main memory every time data is needed. Since data is constantly being worked on, reducing the need to access main memory (which is often slow compared to the ALU and control units) greatly increases the computer's speed.

Computer main memory comes in two principal varieties: random access memory or RAM and read-only memory or ROM. RAM can be read and written to anytime the CPU commands it, but ROM is pre-loaded with data and software that never changes, so the CPU can only read from it. ROM is typically used to store the computer's initial start-up instructions. In general, the contents of RAM is erased when the power to the computer is turned off while ROM retains its data indefinitely. In a PC , the ROM contains a specialized program called the BIOS that orchestrates loading the computer's operating system from the hard disk drive into RAM whenever the computer is turned on or reset. In embedded computers, which frequently do not have disk drives, all of the software required to perform the task may be stored in ROM. Software that is stored in ROM is often called firmware because it is notionally more like hardware than software. Flash memory blurs the distinction between ROM and RAM by retaining data when turned off but being rewritable like RAM. However, flash memory is typically much slower than conventional ROM and RAM so its use is restricted to applications where high speeds are not required.[20]

In more sophisticated computers there may be one or more RAM cache memories which are slower than registers but faster than main memory. Generally computers with this sort of cache are designed to move frequently needed data into the cache automatically, often without the need for any intervention on the programmer's part.

Input/output (I/O)
Main article: Input/output
Hard disks are common I/O devices used with computers.

I/O is the means by which a computer exchanges information with the outside world.[21] Devices that provide input or output to the computer are called peripherals.[22] On a typical personal computer, peripherals include input devices like the keyboard and mouse, and output devices such as the display and printer. Hard disk drives, floppy disk drives and optical disc drives serve as both input and output devices. Computer networking is another form of I/O.

Often, I/O devices are complex computers in their own right with their own CPU and memory. A graphics processing unit might contain fifty or more tiny computers that perform the calculations necessary to display 3D graphics[citation needed]. Modern desktop computers contain many smaller computers that assist the main CPU in performing I/O.

Multitasking
Main article: Computer multitasking

While a computer may be viewed as running one gigantic program stored in its main memory, in some systems it is necessary to give the appearance of running several programs simultaneously. This is achieved by multitasking i.e. having the computer switch rapidly between running each program in turn.[23]

One means by which this is done is with a special signal called an interrupt which can periodically cause the computer to stop executing instructions where it was and do something else instead. By remembering where it was executing prior to the interrupt, the computer can return to that task later. If several programs are running "at the same time", then the interrupt generator might be causing several hundred interrupts per second, causing a program switch each time. Since modern computers typically execute instructions several orders of magnitude faster than human perception, it may appear that many programs are running at the same time even though only one is ever executing in any given instant. This method of multitasking is sometimes termed "time-sharing" since each program is allocated a "slice" of time in turn.[24]

Before the era of cheap computers, the principle use for multitasking was to allow many people to share the same computer.

Seemingly, multitasking would cause a computer that is switching between several programs to run more slowly - in direct proportion to the number of programs it is running. However, most programs spend much of their time waiting for slow input/output devices to complete their tasks. If a program is waiting for the user to click on the mouse or press a key on the keyboard, then it will not take a "time slice" until the event it is waiting for has occurred. This frees up time for other programs to execute so that many programs may be run at the same time without unacceptable speed loss.

Multiprocessing
Main article: Multiprocessing
Cray designed many supercomputers that used multiprocessing heavily.

Some computers may divide their work between one or more separate CPUs, creating a multiprocessing configuration. Traditionally, this technique was utilized only in large and powerful computers such as supercomputers, mainframe computers and servers. However, multiprocessor and multi-core (multiple CPUs on a single integrated circuit) personal and laptop computers have become widely available and are beginning to see increased usage in lower-end markets as a result.

Supercomputers in particular often have highly unique architectures that differ significantly from the basic stored-program architecture and from general purpose computers.[25] They often feature thousands of CPUs, customized high-speed interconnects, and specialized computing hardware. Such designs tend to be useful only for specialized tasks due to the large scale of program organization required to successfully utilize most of the available resources at once. Supercomputers usually see usage in large-scale simulation, graphics rendering, and cryptography applications, as well as with other so-called "embarrassingly parallel" tasks.

Networking and the Internet
Main articles: Computer networking and Internet
Visualization of a portion of the routes on the Internet.

Computers have been used to coordinate information between multiple locations since the 1950s. The U.S. military's SAGE system was the first large-scale example of such a system, which led to a number of special-purpose commercial systems like Sabre.[26]

In the 1970s, computer engineers at research institutions throughout the United States began to link their computers together using telecommunications technology. This effort was funded by ARPA (now DARPA), and the computer network that it produced was called the ARPANET.[27] The technologies that made the Arpanet possible spread and evolved.

In time, the network spread beyond academic and military institutions and became known as the Internet. The emergence of networking involved a redefinition of the nature and boundaries of the computer. Computer operating systems and applications were modified to include the ability to define and access the resources of other computers on the network, such as peripheral devices, stored information, and the like, as extensions of the resources of an individual computer. Initially these facilities were available primarily to people working in high-tech environments, but in the 1990s the spread of applications like e-mail and the World Wide Web, combined with the development of cheap, fast networking technologies like Ethernet and ADSL saw computer networking become almost ubiquitous. In fact, the number of computers that are networked is growing phenomenally. A very large proportion of personal computers regularly connect to the Internet to communicate and receive information. "Wireless" networking, often utilizing mobile phone networks, has meant networking is becoming increasingly ubiquitous even in mobile computing environments.

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Further topics

Hardware
Main article: Computer hardware

The term hardware covers all of those parts of a computer that are tangible objects. Circuits, displays, power supplies, cables, keyboards, printers and mice are all hardware.
History of computing hardware First Generation (Mechanical/Electromechanical) Calculators Antikythera mechanism, Difference Engine, Norden bombsight
Programmable Devices Jacquard loom, Analytical Engine, Harvard Mark I, Z3
Second Generation (Vacuum Tubes) Calculators Atanasoff–Berry Computer, IBM 604, UNIVAC 60, UNIVAC 120
Programmable Devices Colossus, ENIAC, Manchester Small-Scale Experimental Machine, EDSAC, Manchester Mark 1, CSIRAC, EDVAC, UNIVAC I, IBM 701, IBM 702, IBM 650, Z22
Third Generation (Discrete transistors and SSI, MSI, LSI Integrated circuits) Mainframes IBM 7090, IBM 7080, System/360, BUNCH
Minicomputer PDP-8, PDP-11, System/32, System/36
Fourth Generation (VLSI integrated circuits) Minicomputer VAX, IBM System i
4-bit microcomputer Intel 4004, Intel 4040
8-bit microcomputer Intel 8008, Intel 8080, Motorola 6800, Motorola 6809, MOS Technology 6502, Zilog Z80
16-bit microcomputer Intel 8088, Zilog Z8000, WDC 65816/65802
32-bit microcomputer Intel 80386, Pentium, Motorola 68000, ARM architecture
64-bit microcomputer[28] Alpha, MIPS, PA-RISC, PowerPC, SPARC, x86-64
Embedded computer Intel 8048, Intel 8051
Personal computer Desktop computer, Home computer, Laptop computer, Personal digital assistant (PDA), Portable computer, Tablet computer, Wearable computer
Theoretical/experimental Quantum computer, Chemical computer, DNA computing, Optical computer, Spintronics based computer
Other Hardware Topics Peripheral device (Input/output) Input Mouse, Keyboard, Joystick, Image scanner
Output Monitor, Printer
Both Floppy disk drive, Hard disk, Optical disc drive, Teleprinter
Computer busses Short range RS-232, SCSI, PCI, USB
Long range (Computer networking) Ethernet, ATM, FDDI



Software
Main article: Computer software

Software refers to parts of the computer which do not have a material form, such as programs, data, protocols, etc. When software is stored in hardware that cannot easily be modified (such as BIOS ROM in an IBM PC compatible), it is sometimes called "firmware" to indicate that it falls into an uncertain area somewhere between hardware and software.
Computer software Operating system Unix and BSD UNIX System V, AIX, HP-UX, Solaris (SunOS), IRIX, List of BSD operating systems
GNU/Linux List of Linux distributions, Comparison of Linux distributions
Microsoft Windows Windows 95, Windows 98, Windows NT, Windows 2000, Windows XP, Windows Vista, Windows CE
DOS 86-DOS (QDOS), PC-DOS, MS-DOS, FreeDOS
Mac OS Mac OS classic, Mac OS X
Embedded and real-time List of embedded operating systems
Experimental Amoeba, Oberon/Bluebottle, Plan 9 from Bell Labs
Library Multimedia DirectX, OpenGL, OpenAL
Programming library C standard library, Standard template library
Data Protocol TCP/IP, Kermit, FTP, HTTP, SMTP
File format HTML, XML, JPEG, MPEG, PNG
User interface Graphical user interface (WIMP) Microsoft Windows, GNOME, KDE, QNX Photon, CDE, GEM
Text-based user interface Command-line interface, Text user interface
Application Office suite Word processing, Desktop publishing, Presentation program, Database management system, Scheduling & Time management, Spreadsheet, Accounting software
Internet Access Browser, E-mail client, Web server, Mail transfer agent, Instant messaging
Design and manufacturing Computer-aided design, Computer-aided manufacturing, Plant management, Robotic manufacturing, Supply chain management
Graphics Raster graphics editor, Vector graphics editor, 3D modeler, Animation editor, 3D computer graphics, Video editing, Image processing
Audio Digital audio editor, Audio playback, Mixing, Audio synthesis, Computer music
Software Engineering Compiler, Assembler, Interpreter, Debugger, Text Editor, Integrated development environment, Performance analysis, Revision control, Software configuration management
Educational Edutainment, Educational game, Serious game, Flight simulator
Games Strategy, Arcade, Puzzle, Simulation, First-person shooter, Platform, Massively multiplayer, Interactive fiction
Misc Artificial intelligence, Antivirus software, Malware scanner, Installer/Package management systems, File manager

Programming languages

Programming languages provide various ways of specifying programs for computers to run. Unlike natural languages, programming languages are designed to permit no ambiguity and to be concise. They are purely written languages and are often difficult to read aloud. They are generally either translated into machine language by a compiler or an assembler before being run, or translated directly at run time by an interpreter. Sometimes programs are executed by a hybrid method of the two techniques. There are thousands of different programming languages—some intended to be general purpose, others useful only for highly specialized applications.
Programming Languages Lists of programming languages Timeline of programming languages, Categorical list of programming languages, Generational list of programming languages, Alphabetical list of programming languages, Non-English-based programming languages
Commonly used Assembly languages ARM, MIPS, x86
Commonly used High level languages Ada, BASIC, C, C++, C#, COBOL, Fortran, Java, Lisp, Pascal, Object Pascal
Commonly used Scripting languages Bourne script, JavaScript, Python, Ruby, PHP, Perl

Professions and organizations

As the use of computers has spread throughout society, there are an increasing number of careers involving computers. Following the theme of hardware, software and firmware, the brains of people who work in the industry are sometimes known irreverently as wetware or "meatware".
Computer-related professions Hardware-related Electrical engineering, Electronics engineering, Computer engineering, Telecommunications engineering, Optical engineering, Nanoscale engineering
Software-related Computer science, Human-computer interaction, Information technology, Software engineering, Scientific computing, Web design, Desktop publishing

The need for computers to work well together and to be able to exchange information has spawned the need for many standards organizations, clubs and societies of both a formal and informal nature.
Organizations Standards groups ANSI, IEC, IEEE, IETF, ISO, W3C
Professional Societies ACM, ACM Special Interest Groups, IET, IFIP
Free/Open source software groups Free Software Foundation, Mozilla Foundation, Apache Software Foundation

See also
Sister project Look up computer in
Wiktionary, the free dictionary.
Sister project Wikiquote has a collection of quotations related to: Computers
Sister project Wikimedia Commons has media related to: Computer
Sister project Wikiversity has learning materials about Introduction to Computers

* Computability theory
* Computer science
* Computing
* Computers in fiction
* Computer security and Computer insecurity
* Electronic waste
* List of computer term etymologies
* Virtualization


External links

* Computer mini-article

Notes

1. ^ In 1946, ENIAC consumed an estimated 174 kW. By comparison, a typical personal computer may use around 400 W; over four hundred times less. (Kempf 1961)
2. ^ Early computers such as Colossus and ENIAC were able to process between 5 and 100 operations per second. A modern "commodity" microprocessor (as of 2007) can process billions of operations per second, and many of these operations are more complicated and useful than early computer operations.
3. ^ "Heron of Alexandria". http://www.mlahanas.de/Greeks/HeronAlexandria2.htm. Retrieved on 2008-01-15.
4. ^ a b Ancient Discoveries, Episode 11: Ancient Robots, History Channel, http://www.youtube.com/watch?v=rxjbaQl0ad8, retrieved on 2008-09-06
5. ^ Howard R. Turner (1997), Science in Medieval Islam: An Illustrated Introduction, p. 184, University of Texas Press, ISBN 0292781490
6. ^ Donald Routledge Hill, "Mechanical Engineering in the Medieval Near East", Scientific American, May 1991, pp. 64-9 (cf. Donald Routledge Hill, Mechanical Engineering)
7. ^ The Analytical Engine should not be confused with Babbage's difference engine which was a non-programmable mechanical calculator.
8. ^ B. Jack Copeland, ed., Colossus: The Secrets of Bletchley Park's Codebreaking Computers, Oxford University Press, 2006
9. ^ Lavington 1998, p. 37
10. ^ This program was written similarly to those for the PDP-11 minicomputer and shows some typical things a computer can do. All the text after the semicolons are comments for the benefit of human readers. These have no significance to the computer and are ignored. (Digital Equipment Corporation 1972)
11. ^ Attempts are often made to create programs that can overcome this fundamental limitation of computers. Software that mimics learning and adaptation is part of artificial intelligence.
12. ^ It is not universally true that bugs are solely due to programmer oversight. Computer hardware may fail or may itself have a fundamental problem that produces unexpected results in certain situations. For instance, the Pentium FDIV bug caused some Intel microprocessors in the early 1990s to produce inaccurate results for certain floating point division operations. This was caused by a flaw in the microprocessor design and resulted in a partial recall of the affected devices.
13. ^ Even some later computers were commonly programmed directly in machine code. Some minicomputers like the DEC PDP-8 could be programmed directly from a panel of switches. However, this method was usually used only as part of the booting process. Most modern computers boot entirely automatically by reading a boot program from some non-volatile memory.
14. ^ However, there is sometimes some form of machine language compatibility between different computers. An x86-64 compatible microprocessor like the AMD Athlon 64 is able to run most of the same programs that an Intel Core 2 microprocessor can, as well as programs designed for earlier microprocessors like the Intel Pentiums and Intel 80486. This contrasts with very early commercial computers, which were often one-of-a-kind and totally incompatible with other computers.
15. ^ High level languages are also often interpreted rather than compiled. Interpreted languages are translated into machine code on the fly by another program called an interpreter.
16. ^ The control unit's rule in interpreting instructions has varied somewhat in the past. While the control unit is solely responsible for instruction interpretation in most modern computers, this is not always the case. Many computers include some instructions that may only be partially interpreted by the control system and partially interpreted by another device. This is especially the case with specialized computing hardware that may be partially self-contained. For example, EDVAC, the first modern stored program computer to be designed, used a central control unit that only interpreted four instructions. All of the arithmetic-related instructions were passed on to its arithmetic unit and further decoded there.
17. ^ Instructions often occupy more than one memory address, so the program counters usually increases by the number of memory locations required to store one instruction.
18. ^ David J. Eck (2000). The Most Complex Machine: A Survey of Computers and Computing. A K Peters, Ltd.. p. 54. ISBN 9781568811284.
19. ^ Erricos John Kontoghiorghes (2006). Handbook of Parallel Computing and Statistics. CRC Press. p. 45. ISBN 9780824740672.
20. ^ Flash memory also may only be rewritten a limited number of times before wearing out, making it less useful for heavy random access usage. (Verma 1988)
21. ^ Donald Eadie (1968). Introduction to the Basic Computer. Prentice-Hall. p. 12.
22. ^ Arpad Barna; Dan I. Porat (1976). Introduction to Microcomputers and the Microprocessors. Wiley. p. 85. ISBN 9780471050513.
23. ^ Jerry Peek; Grace Todino, John Strang (2002). Learning the UNIX Operating System: A Concise Guide for the New User. O'Reilly. p. 130. ISBN 9780596002619.
24. ^ Gillian M. Davis (2002). Noise Reduction in Speech Applications. CRC Press. p. 111. ISBN 9780849309496.
25. ^ However, it is also very common to construct supercomputers out of many pieces of cheap commodity hardware; usually individual computers connected by networks. These so-called computer clusters can often provide supercomputer performance at a much lower cost than customized designs. While custom architectures are still used for most of the most powerful supercomputers, there has been a proliferation of cluster computers in recent years. (TOP500 2006)
26. ^ Agatha C. Hughes (2000). Systems, Experts, and Computers. MIT Press. p. 161. ISBN 9780262082853. "The experience of SAGE helped make possible the first truly large-scale commercial real-time network: the SABRE computerized airline reservations system..."
27. ^ "A Brief History of the Internet". Internet Society. http://www.isoc.org/internet/history/brief.shtml. Retrieved on 2008-09-20.
28. ^ Most major 64-bit instruction set architectures are extensions of earlier designs. All of the architectures listed in this table, except for Alpha, existed in 32-bit forms before their 64-bit incarnations were introduced.

References

* a Kempf, Karl (1961). Historical Monograph: Electronic Computers Within the Ordnance Corps. Aberdeen Proving Ground (United States Army). http://ed-thelen.org/comp-hist/U-S-Ord-61.html.
* a Phillips, Tony (2000). "The Antikythera Mechanism I". American Mathematical Society. http://www.math.sunysb.edu/~tony/whatsnew/column/antikytheraI-0400/kyth1.html. Retrieved on 2006-04-05.
* a Shannon, Claude Elwood (1940). A symbolic analysis of relay and switching circuits. Massachusetts Institute of Technology. http://hdl.handle.net/1721.1/11173.
* a Digital Equipment Corporation (1972) (PDF). PDP-11/40 Processor Handbook. Maynard, MA: Digital Equipment Corporation. http://bitsavers.vt100.net/dec/www.computer.museum.uq.edu.au_mirror/D-09-30_PDP11-40_Processor_Handbook.pdf.
* a Verma, G.; Mielke, N. (1988). Reliability performance of ETOX based flash memories. IEEE International Reliability Physics Symposium.
* a Meuer, Hans; Strohmaier, Erich; Simon, Horst; Dongarra, Jack (2006-11-13). "Architectures Share Over Time". TOP500. http://www.top500.org/lists/2006/11/overtime/Architectures. Retrieved on 2006-11-27.
* Lavington, Simon (1998), A History of Manchester Computers (2 ed.), Swindon: The British Computer Society, ISBN 0902505018
* Stokes, Jon (2007). Inside the Machine: An Illustrated Introduction to Microprocessors and Computer Architecture. San Francisco: No Starch Press. ISBN 978-1-59327-104-6.

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Personal computer hardware

A personal computer is made up of computer hardware, multiple physical components onto which can be loaded into a multitude of software that perform the functions of the computer.
Typical PC hardware

Though a PC comes in many different form factors, a typical personal computer consists of a case or chassis in a tower shape (desktop) and the following parts:

Motherboard

The motherboard is the "body"[citation needed] of the computer, through which all other components interface. Components directly attached to the motherboard include:

* The central processing unit (CPU) performs most of the calculations which enable a computer to function, and is sometimes referred to as the "brain" of the computer. It is usually cooled by a heat sink and fan.
* The chipset mediates communication between the CPU and the other components of the system, including main memory.
* RAM is the system's main memory or primary storage, and holds data and instructions for running applications and the operating system.
* The BIOS includes boot firmware and power management. The basic input and output tasks from which it gets its name are now handled by operating system drivers.
* Internal Buses connect the CPU to various internal components and to expansion cards for graphics and sound.
o Current
+ The northbridge memory controller, for RAM and PCI Express
# PCI Express, for graphics cards
+ PCI, for other expansion cards
+ SATA, for disk drives
o Obsolete
+ ATA (superseded by SATA)
+ AGP (superseded by PCI Express)
+ VLB VESA Local Bus (superseded by AGP)
+ ISA (expansion card slot format obsolete in PCs, but still used in industrial computers)
* External Bus Controllers support ports for external peripherals. These ports may be controlled directly by the southbridge I/O controller or based on expansion cards attached to the motherboard through the PCI bus.
o USB
o FireWire
o eSATA

[edit] Power supply
Main article: Power supply unit (computer)

Includes power cord, switch, and cooling fan. Supplies power at appropriate voltages to the motherboard and internal disk drives.

[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

* CD (compact disc) - the most common type of removable media, suitable for music and data.
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 12 times as much information. It is the most common way of transferring digital video, and is popular for data storage.
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 Disc - a high-density optical disc format for data and high-definition video. Can store 70 times as much information as a CD.
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 discontinued competitor to the Blu-ray format.
* Floppy disk - an outdated storage device consisting of a thin disk of a flexible magnetic storage medium. Used today mainly for loading RAID drivers.
* 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. Capacities vary, from hundreds of megabytes (in the same ballpark as CDs) to tens of gigabytes (surpassing, at great expense, Blu-ray discs).
* Tape drive - a device that reads and writes data on a magnetic tape, used for long term storage and backups.

[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 and stores data in a digital format.
* RAID array controller - a device to manage several hard disks, to achieve performance or reliability improvement in what is called a RAID array.

[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. Most sound cards, either built-in or added, have surround sound capabilities.

[edit] Networking
Main article: Computer networks

Connects the computer to the Internet and/or other computers.

* Modem - for dial-up connections or sending digital faxes. (outdated)
* Network card - for DSL/Cable internet, and/or connecting to other computers, using the Ethernet cord.
* 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.

[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

* 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 Optical Mouse - a newer technology that uses lasers, or more commonly LEDs to track the surface under the mouse to determine motion of the mouse, to be translated into mouse movements on the screen.
o Trackball - a pointing device consisting of an exposed protruding ball housed in a socket that detects rotation about two axes.

* 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 handheld game controller 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 electrical signals.

[edit] Output
Main article: Output

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

[edit] See also

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