An operating system provides the abstraction of parallel running processes and threads, by alternating the applications to run in parallel. In fact, on systems with a single CPU, there can only be one running thread at a time. While the running thread executes, all the others are waiting in line until the next task switch.
In a cooperative model, switching the task is always a voluntary action requested by the thread implementation. The opposite approach, known as preemption, requires that the kernel periodically interrupts tasks at any point of their execution, to temporarily save the status and resume that of the next task in line.
Switching the running task consists of storing the first store of values of the CPU registers ...
