Computer Hardware

Hardware comprises all of the physical parts of a computer, as distinguished from the data it contains or operates on, and the software that provides instructions for the hardware to accomplish tasks. The boundary between hardware and software is slightly blurry—firmware is software that is "built-in" to the hardware, but such firmware is usually the province of computer programmers and computer engineers in any case and not an issue that computer users need to concern themselves with.

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

Motherboard

A motherboard, also known as main board, logic board or system board, and sometimes abbreviated as mobo, is the central or primary circuit board making up a complex electronic system, such as a computer.

A typical computer is built with the microprocessor, main memory, and other basic components on the motherboard. Other components of the computer such as external storage, control circuits for video display and sound, and peripheral devices are typically attached to the motherboard via connectors or cables of some sort.

Processor

The exact term processor is a sub-system of a data processing system which processes received information after it has been encoded into data by the input sub-system. These data are then processed by the processing sub-system before being sent to the output sub-system where they are decoded back into information. However, in common parlance processor is usually referred to the microprocessor, the brains of the modern day computers. The two major kinds of digital processors are the central processing unit (CPU) and the digital signal processor (DSP).

RAM

Random Access Memory or RAM is a type of computer storage whose contents can be accessed in any order. This is in contrast to sequential memory devices such as magnetic tapes, discs and drums, in which the mechanical movement of the storage medium forces the computer to access data in a fixed order. It is usually implied that RAM can be both written to and read from, in contrast to Read-Only Memory or ROM. RAM is usually used for primary storage in computers to hold actively-used and actively-changing information, although some devices use certain types of RAM to provide long term secondary storage.

Buses

The Peripheral Component Interconnect standard (in practice almost always shortened to PCI) specifies a computer bus for attaching peripheral devices to a computer motherboard. These devices can take the form of:

* integrated circuits fitted on the motherboard itself (called planar devices in the PCI specification); or

* expansion cards that fit in sockets.

The PCI bus occurs commonly in PCs, where it has displaced ISA and VESA Local Bus as the standard expansion bus, but it also appears in many other computer types.

The PCI specification covers the physical size of the bus (including wire spacing), electrical characteristics, bus timing and protocols. The specification can be purchased from the PCI Special Interest Group (PCISIG).

PCI Express

PCI Express (formerly known as 3GIO for 3rd Generation I/O, not to be mistaken with PCI-X) is an implementation of the PCI computer bus that uses existing PCI programming concepts and communications standards, but bases it on a much faster serial communications system. It is being supported primarily by Intel, who started working on the standard as the Arapahoe project after pulling out of the InfiniBand system.

PCI Express is intended to be used as a local bus only. Due to it being based on the existing PCI system, cards and systems can be converted to PCI Express by changing the physical layer only – existing systems could be re-booted on PCI Express and never even know it. The higher speeds on PCI Express allow it to replace almost all existing internal buses, including AGP and PCI, and Intel envisions a single PCI Express controller talking to all external devices, as opposed to the northbridge/southbridge solution in current machines.

USB

Universal Serial Bus (USB) provides a serial bus standard for connecting devices, usually to a computer, but it also is in use on other devices such as set-top boxes, game consoles and PDAs.

Accelerated Graphics Port

The Accelerated Graphics Port (also called Advanced Graphics Port) is a high-speed point-to-point channel for attaching a single device (generally a graphics card) to a computer's motherboard, primarily to assist in the acceleration of 3D computer graphics. Many classify AGP as a type of computer bus, but this is something of a misnomer since buses generally allow multiple devices to be connected, while AGP does not. Some motherboards have been built with multiple independent AGP slots.

Hard Disk

A hard disk (or "hard disc" or "hard drive" or "hard disk drive") is a computer storage device that stores data on rotating magnetic surfaces. A hard disk uses rigid rotating platters. It stores and retrieves digital data from a planar magnetic surface. Information is written to the disk by transmitting an electromagnetic flux through an antenna or write head that is very close to a magnetic material, which in turn changes its polarization due to the flux. The information can be read back in a reverse manner, as the magnetic fields cause electrical change in the coil or read head that passes over it.

Floppy Disk

A floppy disk is a data storage device that is composed of a circular piece of thin, flexible (i.e. "floppy") magnetic storage medium encased in a square or rectangular plastic wallet. Floppy disks are read and written by a floppy disk drive or FDD, the latter acronym not to be confused with "fixed disk drive", which is an old IBM term for a hard disk drive.

CD

A compact disc (or CD) is an optical disc used to store digital data, originally developed for storing digital audio. A standard compact disc, often known as an audio CD to differentiate it from later variants, stores audio data in a format compliant with the red book standard. An audio CD consists of several stereo tracks stored using 16-bit PCM coding at a sampling rate of 44.1 kHz. Most compact discs have a diameter of 120 mm, which is designed to hold 74 minutes of audio, and in practice slightly more.

Compact disc technology was later adapted for use as a data storage device, known as a CD-ROM.

CD-ROM

The CD-ROM (an abbreviation for "Compact Disc Read-Only Memory" (ROM)) is a non-volatile optical data storage medium using the same physical format as audio compact discs, readable by a computer with a CD-ROM drive. A CD-ROM is a flat, plastic disc with digital information encoded on it in a spiral from the center to the limit, the outside edge. The CD-ROM Yellow Book standard was established in 1985 by Sony and Philips. Microsoft and Apple Computer were early enthusiasts and promoters of CD-ROMs. John Sculley, CEO of Apple at the time, said as early as 1987 that the CD-ROM would revolutionize the use of personal computers.

CD-ROM reading devices are a standard component of most modern personal computers. In general, audio CDs are distinct from CD-ROMs, and CD players intended for listening to audio cannot make sense of the data on a CD-ROM, though personal computers can generally play audio CDs. It is possible to produce composite CDs containing both data and audio with the latter capable of being played on a CD player, whilst data or perhaps video can be viewed on a computer.

CD-RW

In computing and data storage, Compact Disc Rewritable, or CD-RW, is a rewritable version of CD-ROM. Whereas standard prerecorded compact discs have their information permanently stamped into an aluminium reflecting layer, CD-RW discs have a phase-change recording layer and an additional aluminium reflecting layer. A laser beam can melt crystals in the recording layer into a non-crystalline amorphous phase, or anneal them slowly at a lower temperature back to the crystalline state. The different reflectance of the resulting areas make them appear like the 'pits' and 'lands' of a standard CD.

A CD-RW drive can write about 700MiB of data to CD-RW media around 1000 times. The number of times the CD-RW can be re-written varies depending on the quality and production techniques employed. Most CD-RW drives can also write once to CD-R media. Except for the ability to completely erase a disc, CD-RWs act very much like CD-Rs and are subject to the same restrictions

Note that unlike CD-Rs, CD-RW discs are non-standard, in that they do not meet the Orange Book standards for CDs. Hence CD-RW media cannot be read by CD-ROM drives built prior to 1997 due to the reduced reflectivity (15% compared to 70%) of CD-RW media. CD-RW is also more expensive than CD-R, and so CD-R is sometimes considered a better technology for archival purposes.

CD-R

A CD-R (Compact Disc-Recordable) is a thin (1.2 mm) disc made of polycarbonate with a 120 mm or 80 mm diameter that is mainly used to store music or data. However, unlike conventional CD media, a CD-R has a core of dye instead of metal.

A standard CD-R has a storage capacity of 74 minutes of audio or 650MB of data (though MB is printed on CDs as the binary prefixes haven't caught on in the industry, MB will be used in this article). Non-standard CD-Rs are available with capacities of 80 minutes/703MB, which they achieve by exceeding the tolerances specified in the Orange Book CD standards. Most CD-Rs on the market are of the latter capacity. There are also 90 minute/790MB and 99 minute/870MB discs, though they are rare.

A specially designed type of CD-ROM drive, called a CD-R drive, CD burner, or CD writer can be used to write CD-Rs. A laser is used to etch ("burn") small pits into the dye so that the disc can later be read by the laser in a CD-ROM drive or CD player. The laser used to write CD-Rs is an infrared laser which emits laser radiation at a wavelength of 780 nm. The reflectivity in the pit area is different (lower) than for the unchanged dye area, because the refractive index of the dye is lowered upon "burning" a pit. Upon reading back the stored information, the laser operates at a low enough power not to "burn" the dye and an optical pick-up records the changes in the intensity of the reflected laser radiation when scanning along the groove and over the pits. The change of the intensity of the reflected laser radiation is transformed into an electrical signal, from which the digital information is recovered ("decoded"). The decomposition of the dye in the pit area through the heat of the laser is irreversible (permanent). Therefore, once a section of a CD-R is written, it cannot be erased or rewritten, unlike a CD-RW. A CD-R can be recorded in multiple sessions.

When looked at by the naked eye, the part of the CD-R which contains data will be slightly darker than areas which are not written to. Using this method, you can get a rough estimation of the amount of data on a CD-R, and whether or not it has been written to.

Sound Card

A sound card is a computer expansion card that can input and output sound under program control. A typical sound card includes a sound chip usually featuring a digital-to-analog converter that converts recorded or generated digital waveforms of sound into an analog format. This signal is led to a (earphone-type) connector where a cable to an amplifier or similar sound destination can be plugged in.

More advanced designs usually include more than one sound chips, and separate between synthesized sounds (usually for real-time generation of music and special effects with little amounts of data and CPU time and perhaps MIDI compatibility) and digital sound reproduction.

The latter is usually achieved by multi-channel DACs, able to play multiple digital samples at different pitches and perhaps even applying real-time effects to them, like filtering or distortion. Sometimes, multi-channel digital sound playback can also be used for music synthesis if used with a digitized instrument bank of some sort, typically a small amount of ROM or Flash memory containing samples corresponding to the standard MIDI instruments.

"Audio codecs" on the other hand rely heavily on software for music synthesis, MIDI compliance and even multiple-channel emulation, their purpose being to simplify the design of costs of the sound card itself.

Also, most sound cards have a "line in" connector where the sound signal from a cassette tape recorder or similar sound source can be connected to. The sound card can digitize this signal and store it (controlled by the corresponding computer software) on the computer's hard disk.

The third external connector a typical sound card has, is used to connect a microphone directly. Its sound can be recorded to hard disk or otherwise processed (for example, by speech recognition software or for Voice over IP).

Modem

A modem (a portmanteau word constructed from modulator and demodulator) is a device that modulates an analog carrier signal (sound), to encode digital information, and that also demodulates such a carrier signal to decode the transmitted information. Put simply, it turns the digital '1s and 0s' into sounds that can be transmitted over the Plain Old Telephone System (POTS), and once received on the other side, converts those sounds back into 1s and 0s. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data. Primarily used to communicate via telephone lines, modems can be used over any means of transmitting analog signals, from driven diodes to radio.

Network Card

A network card (also called network adapter, network interface card, NIC, etc.) is a piece of computer hardware designed to provide for computer communication over a computer network.

The card implements the electronic circuitry required to communicate using a specific physical layer and data link layer standard such as ethernet or token ring. This provides a base for a full network protocol stack, allowing communication among small groups of computers on the same LAN and large-scale network communications through routable protocols, such as IP.

A network card typically has a twisted pair, BNC, or AUI socket where the network cable is connected, and a few LEDs to inform the user of whether the network is active, and whether or not there is data being transmitted on it.

Most newer computers have a network interface built into the motherboard, so a separate network card is not required unless multiple interfaces are needed or some other type of network is used.

Computer Keyboard

A computer keyboard is a peripheral modelled after the typewriter keyboard. Keyboards are designed for the input of written text, and also to control the operation of the computer. Physically, computer keyboards are an arrangement of rectangular or near-rectangular buttons, or "keys". Keyboards typically have characters engraved or printed on the keys; in most cases, each press of a key corresponds to a single written symbol. However, to produce some symbols requires pressing and holding several keys simultaneously, or in sequence; other keys do not produce any symbol, but instead affect the operation of the computer, or the keyboard itself. See input method editor.

A wireless keyboard has no direct connection to the computer. The keyboard presses are conveyed by radio to a small local receiver, which is connected to the computer.

Mouse

A mouse is a handheld pointing device for computers, involving a small object fitted with one or more buttons and shaped to sit naturally under the hand. The underside of the mouse houses a device that detects the mouse's motion relative to the flat surface on which it sits. The mouse's 2D motion is typically translated into the motion of a cursor on the display.

It is called a mouse primarily because the cord on early models resembled the rodent's tail, and also because the motion of the pointer on the screen can be mouselike. In popular usage, the plural can be either mice or mouses. See English plural for more information.

Scanner

A scanner is a device which analyzes a physical image (such as a photograph, printed text, or handwriting) or an object (such as ornament) and converts it to a digital image. Most scanners today are variations on the desktop (or flatbed) scanner. Hand-held scanners, where the device is moved by hand, were briefly popular but are now not used due to the impossibility of obtaining a high-quality image. Both these types of scanners use a CCD as the image sensor, whereas a drum scanner uses a photomultiplier tube (PMT) as the image sensor.

Web Camera

A web camera (or webcam) is a real time camera whose images can be accessed using the World Wide Web, instant messaging, or a PC video calling application. Generally, a digital camera delivers images to a web server, either continuously or at regular intervals.

A webcam is also the name of a class of video camera devices which connect directly to the PC for the purpose of video calling over the internet.

Computer Printer

A computer printer is a computer peripheral device that produces a hard copy (permanent human-readable text and/or graphics, usually on paper) from data stored in a computer connected to it.

Monochrome, color and photo printers

A monochrome printer can only produce an image consisting of one color, usually black. A monochrome printer may also be able to produce graduations of tone of that color, such as a grey-scale.

A color printer can produce images of multiple colors.

A photo printer is a color printer that can produce images that mimic the color range (gamut) and resolution of photographic methods of printing.

Methods of image creation

Toner-based printers

Laser printers refer to the method used to adhere toner to the media. The advent of cost-effective, precision lasers has made them the dominant toner-based monochrome printer type for home and office applications. Another toner based printer is the LED printer which uses an array of LED's instead of a laser to cause toner adhesion.

Ink jet printers

Ink jet printers spray very small, precise amounts (usually a few picolitres) of ink onto the media. For color applications including photo printing, ink jet methods are dominant.

Impact Printers

Impact printers rely on a forcible impact to transfer ink to the media, similar to typewriters, that are typically limited to reproducing text. A daisy wheel printer is a specific type of impact printer where the type is carried on a wheel.

Dot-matrix printers

In the general sense many printers rely on a matrix of pixels, or dots, that together form the larger image. However, the term dot matrix printer is specifically used for impact printers that use a matrix of small pins to create precise dots. The advantage of dot-matrix over other impact printers is that they can produce graphical images in addition to text; however the text is generally of poorer quality than type-based impact printers.