Process scheduling is one way for a processor to handle n processes, by scheduling the execution process. Each process is executed one by one according to prescribed schedule.
The aim of processor scheduling is to assign processes to be executed by the processor or processors over time, in a way that meets system objectives, such as response time, throughput and processor efficiency. In many systems, this scheduling activity is broken down into three separate functions: long, medium and short-term scheduling.
Types of Scheduling
Long term Scheduling
The long term scheduler determines which programs are admitted to the system for processing. Thus, it controls the degree of multiprogramming. Once admitted a job or user program becomes a process and added to the queue for the short term scheduler. In some systems, a newly created process begins in a swapped-out condition, in which case it is added to the queue for the medium term scheduler.
Medium term scheduling
Medium term scheduling is a part of the swapping function. The swapping in decision is based on the need to manage the degree of multiprogramming.
It is the decision to add to the number of processes that are partially of fully in main memory.
Short term scheduling
The short term scheduler is also known as the dispatcher executes must frequently and makes the fine grained decision of which process to execute next.
It is the decision as to which available process will be executed by the processor.
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