As fast as required. A real-time system must respond to a signal, event or request fast enough to satisfy some requirement. For example, space flight computers must respond to changing conditions to keep a rocket on course. Industrial robots must keep an assembly line moving. Vehicle accident prevention systems must respond to road conditions immediately.
The term is not used as much with business applications, but in the past, when terminals first appeared on office desks, a description for an online, real-time business system was common. See
embedded system,
real-time audio,
real-time video,
real-time clock and
real-time search.
Real-Time Communications
Videoconferencing and gaming require real-time systems because there can be no delay whatsoever. Response times are measured in milliseconds. For gaming, the system must render new video frames the instant the user presses a button on the game controller.
It's Real Time All the Time
The Internet has delivered us the real-time world, where we expect an almost-immediate answer to every question we ask. The difference is time. Is the response in microseconds (real real-time systems) or seconds (everyday use of computers)?