(1) A communications technique that determines when a terminal is ready to send data. The computer continually interrogates its connected terminals in a round robin sequence. If a terminal has data to send, it sends back an acknowledgment and the transmission begins. Contrast with an interrupt-driven system, in which the terminal generates a signal when it has data to send.
(2) A technique that continually interrogates a peripheral device to see if it has data to transfer. For example, if a mouse button was pressed or if data are available at a communications port. Contrast with event-driven or interrupt-driven techniques, in which the operating system generates a signal and interrupts the system.