computer

computer An electronic tool that manipulates information in accordance with a predefined sequence of instructions. Computers have a simple ‘brain’, called the central processing unit (CPU), that can do arithmetic and take decisions based on the results, and a memory, which stores the instructions and information. Strictly speaking, all other parts of a computer system are peripheral devices, but in practice all computers have at least: an input device, such as a keyboard, by means of which the information is fed in; an output device, such as a screen or printer, which displays the results of their work; and extra memory in the form of magnetic disks or magnetic tape, called backing store. Inside a computer, both information and instructions are represented by binary numbers (see binary notation) and all processing is done using these numbers. A computer needs to be given detailed instructions, called a program, before it can perform even the simplest task. The art of composing these instructions is called computer programming. The general term for the programs that a computer needs in order to operate is software, while the computer and devices attached to it are called hardware.

Traditionally, computers have been classified into three types according to size. The largest is the mainframe, used typically for large-scale corporate data processing; and the smallest is the personal computer, designed for a single user. Between these extremes is the minicomputer. These distinctions have become blurred, as minicomputers and personal computers become more powerful. Moreover, mainframe and minicomputers have been replaced in many situations by groups of personal computers linked to form local area networks.