How does the OS scheduler regain control of CPU?

Question

I recently started to learn how the CPU and the operating system works, and I am bit confused about the operation of a single-CPU machine with an operating system that provi

Answer 1

The OS sets up a hardware timer (Programmable interval timer or PIT) that generates an interrupt every N milliseconds. That interrupt is delivered to the kernel and user-code is interrupted.

It works like any other hardware interrupt. For example your disk will force a switch to the kernel when it has completed an IO.