ATing system> (I/O) CommunicATion between a computer and its users, its storage devices, other computers (via a network) or the outside world. The devices the computer uses to do this are called "peripherals". WhAT actually counts as I/O depends on whAT level of detail you are considering, e.g. communicATion between processors would not be considered I/O when considering a multiprocessor as a single system. Important aspects of I/O are throughput, lATency, and whether the communicATions is synchronous or asynchronous (using some kind of buffer). (2003-12-04)