Special-Purpose Digital Computer

a digital computer designed to solve a narrow range of problems. Special-purpose computers are simpler and cheaper than general-purpose computers but have more limited logical and computational capabilities.

In special-purpose computers, the logical structure, instruction repertory, and data input-output devices are adapted to solve strictly defined problems as efficiently as possible. The instruction repertory is most often of the one-address type and involves a limited number of operations. Numbers are usually represented in fixed-point form; the number of binary digits used is comparatively small: up to 20–25. Special-purpose computers are generally designed to solve problems repeatedly in accordance with previously prepared programs while periodic or continuous changes occur in the input data. In order to ensure high computer speed and reliability, the programs are stored in nonvolatile memory units.

Special-purpose computers are often equipped with analogue-to-digital converters, state locks, timers, switches for signals from external sources, display units, lighted panel indicators, and plotters. The design of a particular special-purpose computer depends on the conditions in which the computer is to be used. For example, computers on board spacecraft and aircraft should combine high efficiency and reliability with small size and weight. Such computers should consume a minimum of energy and be capable of operating under sharply variable climatic and mechanical conditions.

The principal area of application of special-purpose computers is automatic control systems. Special-purpose computers can be effectively used in combination with general-purpose computers—for example, to solve special problems in the preparation and processing of information and to solve problems in the simulation of various processes.