The OS present inside the embedded devices is called an RTOS (Real-Time Operating System). In embedded devices, real-time tasks are critical where timing plays a very important role. Real-time tasks are Time Deterministic means the response time to any event is always constant so that it can be guaranteed that any particular event will occur at a fixed time. RTOS is designed to run applications with very precise timing and a high degree of reliability. RTOS also helps in multi-tasking with a single core.
[original story: Circuit Digest]