Switching Processes
Posted on
A CPU can only execute one program at a time. Once a program is running on the CPU, the OS is effectively not running. So how can it take back control over the system?
Cooperative approach
In this model, the OS trusts processes to periodically give back control to the OS. Also, every time a process makes system calls or performs illegal actions, the OS regains control. But if a process ever gets stuck (with malicious intent or not), the only way to free the system is to reboot it.
Interrupt on a timer
Instead of trusting programs to behave reasonably, we can enforce periodical OS control by sending interrupts on a timer. An interrupt handler runs at certain intervals at all times to give the OS a chance to make scheduling decisions. The timer is started at boot time.
Tags: programming ostep