What are short, long and medium-term scheduling?

Long term scheduler verifies which programs are admitted to the system for processing. It controls the degree of multiprogramming. Once admitted, a job becomes a process.

Medium term scheduling is part of the swapping function. This relates to processes that are in a blocked or suspended state. They are swapped out of real-memory unless they are ready to execute. The swapping-in decision is based on memory-management criteria.

Short term scheduler, also known as a dispatcher executes most often, and makes the finest-grained decision of which process should implement next. This scheduler is invoked whenever an event occurs. It may lead to interruption of one process by preemption.