<P> A real - time operating system (RTOS) is an operating system (OS) intended to serve real - time applications that process data as it comes in, typically without buffer delays . Processing time requirements (including any OS delay) are measured in tenths of seconds or shorter increments of time . A real time system is a time bound system which has well defined fixed time constraints . Processing must be done within the defined constraints or the system will fail . They either are event driven or time sharing . Event driven systems switch between tasks based on their priorities while time sharing systems switch the task based on clock interrupts . Most RTOS's use a pre-emptive scheduling algorithm . </P> <P> 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 . 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 . </P> <P> An RTOS 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; 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 . </P>

A required characteristic of an online real-time system is