Short-term processor scheduler

Preemption & non-preemption

The short-term processor scheduler can be preemptive or non-preemptive.

Non-preemptive scheduling

A process keeps the processor until it blocks or ends.

• Transitions time-out and preempt do not exist.

• Typical in batch systems. Why?

Preemptive scheduling

A process can lose the processor due to external reasons.

• by exhaustion of the assigned time quantum (time-out transition).

• because a more priority process becomes ready to run (preempt transition).

Interactive systems must be preemptive. Why?

What type to use in a real-time system? Why?