Real-time operating system

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A real-time operating system (RTOS) is an operating system (OS) intended to serve real-time application requests.

A key characteristic of an RTOS is the level of its consistency concerning the amount of time it takes to accept and complete an application's task; the variability is jitter[1]. A hard real-time operating system has less jitter than a soft real-time operating system. The chief design goal is not high throughput, but rather a guarantee of a soft or hard performance category. An RTOS that can usually or generally meet a deadline is a soft real-time OS, but if it can meet a deadline deterministically it is a hard real-time OS.[citation needed]

A real-time OS has an advanced algorithm for scheduling. Scheduler flexibility enables a wider, computer-system orchestration of process priorities, but a real-time OS is more frequently dedicated to a narrow set of applications. Key factors in a real-time OS are minimal interrupt latency and minimal thread switching latency, but a real-time OS is valued more for how quickly or how predictably it can respond than for the amount of work it can perform in a given period of time.[2]


Design philosophies

The most common designs are:

  • Event-driven which switches tasks only when an event of higher priority needs service, called preemptive priority, or priority scheduling.
  • Time-sharing designs switch tasks on a regular clock interrupt, and on events, called round robin.

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