Process Scheduling

• 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

>Device queues – set of processes waiting for an I/O device.

>Processes migrate between the various queues.

• Schedules

>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.

• Control 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 support.