computer

Programmable electronic device that processes data and performs calculations and other symbol-manipulation tasks. There are three types: the digital computer, which manipulates information coded as binary numbers (see binary number system); the analogue computer, which works with continuously varying quantities; and the hybrid computer, which has characteristics of both analogue and digital computers. In common usage, when someone refers to a ‘computer’, they tend to mean a digital computer.

There are four types of digital computer, corresponding roughly to their size and intended use. Microcomputers (personal computers, or PCs) are the smallest and most common, used at home, in small businesses, and in schools. They are usually single-user machines. Minicomputers (or mid-range computers) are found in medium-sized businesses and university departments. They may support from around 10 to 200 users at once, although these have now largely been replaced by networks of microcomputers. Mainframes (or enterprise servers), which can often service many hundreds of users simultaneously, are found in large organizations, such as national companies and government departments. Supercomputers are mostly used for highly complex scientific tasks, such as analysing the results of nuclear physics experiments and weather forecasting.