This paper is intended as an introduction to computers and computer devices for those who are not familiar with them, and in particular with their applications to measurement and control.

There are many possible ways to define a computer, but perhaps the most general is that a computer is a device that stores and manipulates patterns and communicates them with the `outside world'. The most familiar use of computers is as glorified calculators, and although the need to do calculations rapidly and accurately was one of the major driving forces behind their development, modern computers have more general applications. The early electronic computers, for example, were developed for code breaking in the last warclearly pattern matching rather than calculation. The arithmetic capabilities of computers have received much attention and have been developed to a very high level, but most computers these days spend only a minute proportion of their time doing arithmeticÐthe rest is taken up with text handling, communication, and translation of high level languages into `machine code'.