Computer Input/Output Port
John A. Watson · 1985
One of the most useful additions to a home computer is an input/ output port. This enables the computer to communicate with the outside world, by switching things on and off, and by reading the state of input lines. It is possible to buy ready-made input/output ports for most of the popular microcomputers, but they are not particularly cheap; often the price is an appreciable fraction of the original cost of the computer itself. Such accessories generally use a special-purpose I/O chip, capable of controlling perhaps 24 lines, and with added features for ‘handshaking’ and interrupt handling. But all these features may not be needed.