Process Scheduling

a). Process Scheduling Queues

• Job queue – set of all processes in the system.
• Ready queue – set of all processes residing in main memory, ready and waiting to execute.
• Device queues – set of processes waiting for an I/O device. Processes migrate between the various queues.

b). Schedulers

• Long-term scheduler (or job scheduler) – selects which processes should be brought into the ready queue.
• Short-term scheduler (or CPU scheduler) – selects which process should be executed next and allocates CPU.

c). Context Switch

• When CPU switches to another process, the system must save the state of the old process and load the saved state for the new process. Context-switch time is overhead; the system does no useful work while switching. Time dependent on hardware suppor