How Does the Operating System Get Back Control of a Processor?

The operating system should insure that the processes are allocated memory and system resources in a fair and equitable way, so that no one process can hoggle the resources for itself. And it also needs to keep track of which of them is currently running and when each of them was last run,. The answer is a bit sneaky, because there are a couple of ways the operating system can get back from a process. One way is whenever the process performs a system call. Another way is whenever an interrupt is raised by i o.