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Asked: 2026-05-20T14:42:48+00:00

I just realized that after learning a lot about various scheduling algorithms, how a

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I just realized that after learning a lot about various scheduling algorithms, how a context switch is done, etc. one thing still isn’t clear to me.

Take a uniprocessor system:

If process A is running and it’s time slot should end in 5 seconds, how does the scheduler or the operating system know how to end it after 5 seconds? No part of the operating system can run while A is running. The scheduler is supposed to be monitoring it, but how can it if it cannot run? Does the operating system’s scheduler write an ISR and have an interrupt generate every 5 seconds? Is this possible? Even if it is, it doesn’t seem a good way to implement it.

How exactly does a scheduler do this?

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  1. Editorial Team

    Does the operating system’s scheduler write an ISR and have an interrupt generate every 5 seconds? Is this possible? Even if it is, it doesn’t seem a good way to implement it.

    Yes, this is exactly how it works on a preemptive multitasking system (although on desktop systems the interval is usually more like 10 milliseconds).

    Yes, there are other schemes, such as cooperative multitasking, where each process decides for itself when to yield.

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