Real-time operating system

A real-time operating system, or RTOS, is an operating system built for applications that process data and events under critically defined time constraints. It mostly targets resource constrained devices such as microcontrollers and differs from a time-sharing system such as Unix, which divides resources with a scheduler and fixed task priorities. Every operation must verifiably finish within its time and resource limits or the system fails safe. An RTOS is event-driven and preemptive, so it can watch the relative priority of competing tasks and change them. Its key quality is consistency in how long it takes to accept and complete a task; the variation is called jitter. A system that usually meets deadlines is soft real-time, and one that meets them deterministically is hard real-time. Designs include event-driven priority scheduling and time-sharing round-robin switching.