Peripherals | Research & Encyclopedia Articles

Peripherals

A computer as a whole consists of both hardware and software. The hardware includes such items as the central processing unit (CPU); the computer's primary storage, random-access memory (RAM); and other hardware devices such as disk drives, monitor, keyboard, printer, and the like. Of these, all hardware devices other than the CPU and the RAM are generically referred to as peripherals. The use of this term reflects a great bias in computer architecture and hardware design, where the CPU and its immediate environment are considered to be central to computing, and everything else is merely an object in the periphery. To some extent it is sensible to give importance to the CPU, of course, but there also a case to be made for why the excessive fixation on the CPU is unhealthy. It is certainly true that peripherals have improved little over the years compared with the tremendous advances made by CPUs over the same time, so much so that a quantum leap in computer performance would probably occur more by improving the performance of peripherals than anything else.

A computer is traditionally held to perform four functions that are characteristic of it--any device that performs these functions is a computer, and any that does not, is not. These functions are input, processing, output, and storage. Of these, processing is the province of the CPU, aided by the RAM, and the others are the province of the peripherals.

Input and output are generally done by peripherals that interact with humans, and must either convert data given by humans into computer-accessible form, or else must present the results of computation in a form that humans find useful. The most common peripherals used for input are devices such as keyboard, mouse, joystick, microphone, touch-screen, and so on. In special circumstances, such as computers that are designed to work with physically challenged people, or computers that are designed to work with industrial equipment, we may have other kinds of peripherals that are used for input.

Peripherals that produce output for humans are most commonly of two kinds, those that produce screen output, or those that produce paper output. Screen output is most commonly preferred in case of non-final results, where the results of change must be continually updated on an ongoing basis. Screen output devices are commonly called monitors, and are of two major kinds: cathode ray tube (CRT) and liquid crystal display (LCD). CRT monitors use largely the same technology as household television sets, although they have a much higher resolution. They are generally much heavier, use more power, and are part of non-portable desktop machines. LCD monitors are lighter, and are similar to displays used on digital wristwatches or portable calculators. They are lighter and are hence used in portable handheld and laptop devices, use much less power and hence can be supplied by battery, and are more expensive.

Paper output via peripherals comes largely from printers, which themselves are of two major kinds: impact and non-impact. In case of impact printers, there is a physical impact of a print head or some such device against the sheet of paper on which the printed impression is to be conveyed. Examples of impact printers include dot-matrix printers, current into the early 1990s but now mostly gone, and line printers, which were used in the 1960s and later but are nowhere used now. Impact printers were standard technology upto the 1970s, but have lost favor since. Part of the reason for this is that owing to their large numbers of moving parts, they suffer greater wear and tear and have greater need for maintenance. The print quality is also often not very good, and is restricted besides to certain font styles or sizes, which is an inconvenient restriction for desktop publishing, high quality typesetting, or when working with images, graphics, or foreign language material. Impact printers can also be quite noisy, which restricts their use in environments where noise is undesirable. Non-impact printers, such as laser printers, have become the standard technology, as they remedy all these ills.

Peripherals for storage are the secondary (persistent) storage devices on which it is possible to store data that survives even after the computer is turned off. Storage devices in common use can be classified in either of two ways: as using magnetic storage versus optical storage, or as offering sequential access versus random access. Magnetic storage devices, such as hard drives, disk drives, and tape drives record the information to be stored in the form of magnetic fields generated in a suitably designed stable artifact such as a diskette or a cassette tape, and by reading these magnetic fields when the diskette or cassette is played back, it is possible to recover the data that was encoded. Optical storage typically is in the form of using laser beams to record and read bits (0s and 1s) of information. Magnetic storage media are susceptible to distortion or loss by exposure to strong electric or magnetic fields, but have the advantage that they can be erased and re-written relatively easily. Optical storage is generally more reliable, but optical media may be harder to write to, and may not allow for as many erasures and re-writes as magnetic media do.

Sequential access is the restriction that data can only be read in the exact sequence in which they were recorded; an example of this is cassette tape drives, where the tape has to be forwarded or rewound to access non-contiguous data. Cassette players for music have largely given way to CD players because people have found that it is a hassle to have to rewind or fast-forward the tape when one wants to listen to songs in some arbitrary order of personal choice. For like reason, tape drives are no longer the mainstay of secondary storage, and are used only for limited purposes like creating system backups that do not have to be accessed at random. Random access devices such as hard drives and CD drives are suitable for most uses where individual items stored need to be read.