A real-time system is one in which the correctness of a computation depends not only on the logical result but also on the time at which the result is produced. When an airbag sensor detects a collision, the system must trigger the deployment within a strictly defined millisecond window. Speed is necessary, but the predictability of that speed is paramount.
Interrupt Service Routines (ISRs) should be microscopic. A real-time system is one in which the