In an operating system, there is a module called the scheduler, which schedules different tasks and determines when a process will execute on the processor. This way, the multi-tasking is achieved. The scheduler in a Real Time Operating System (RTOS) is designed to provide a predictable execution pattern. In an embedded system, a certain event must be entertained in strictly defined time.

To meet real time requirements, the behaviour of the scheduler must be predictable. This type of OS which have a scheduler with predictable execution pattern is called Real Time OS(RTOS). The features of an RTOS are

☛ Context switching latency should be short.

☛ Interrupt latency should be short.

☛ Interrupt dispatch latency should be short.

☛ Reliable and time bound inter process mechanisms.

☛ Should support kernel preemption.