asynchronous communication This term describes how your computer uses a modem to connect with other computers. Back in the days of teletypes and dumb terminals, computers sent data synchronously--they operated using a shared timer that marked the transmission of each character. This didn't work very efficiently for large blocks of data over phone lines, however. So modern modems use asynchronous rules: instead of synching up to a time signal to mark a character, transmitting computers use a start bit, a stop bit, and an optional error-checking parity bit to indicate to receiving computers the boundary of each character. (The term is a bit of a misnomer, though, since all modems synch up with one another before they transmit data.) See also: start bit, stop bit, parity bit