n. an electronic device that carries out arithmetical and logical operations in accordance with a precise sequence of instructions (a program) and so can process data or carry out any task that can be expressed in such a way. Although there are analogue devices that qualify as computers, it is typically a digital computer with a number of separate parts: an input device such as a keyboard, a central processing unit (cpu) consisting of a large number of logic gates, memory units such as disks or magnetic tapes, and output devices such as a visual display unit and a printer. Automata theory and complexity theory are concerned not with the physical properties of actual computers, but with the theoretical capabilities of abstract machines, defined in terms of their programs.