Difference Between Long Term Short Term and Medium Term Scheduler

Difference Between Long Term Short Term and Medium Term Scheduler in Tabular Form

  • Summary: Schedulers are special system software that handles process scheduling in various ways. Their main task is to select the job to decide which process to run first.
  • Schedulers are Three types:
    1. Long Term Scheduler
    2. Short Term Scheduler
    3. Medium Term Scheduler
  • Long Term Scheduler is also called job scheduler. Short Term Scheduler is also called CPU scheduler. Medium term scheduling is part of the swapping.

Comparison Chart

Long Term Short Term Medium Term
It is a job scheduler. It is a CPU scheduler. It is swapping.
Speed is less than short term scheduler. Speed is very fast. Speed is in between both
It controls the degree of multiprogramming. Less control over the degree of multiprogramming. Reduce the degree of multiprogramming.
Absent or minimal in a time-sharing system. Minimal in a time-sharing system. Time-sharing system uses a medium-term scheduler.
It selects processes from the pool and load them into memory for execution. It selects from among the processes that are ready to execute. Process can be reintroduced into the meat and its execution can be continued.
Process state is (New to Ready). Process state is (Ready to Running) –
Select a good prccess, mix of I/O bound, and CPU bound. Select a new process for a CPU quite frequently. –




Long Term Scheduler

  • It is also called job scheduler.
  • Long term scheduler determines which programs are admitted to the system for processing.
  • Job scheduler selects processes from the queue and loads them into memory for execution.
  • Process loads into the memory for CPU scheduling. The primary objective of the job scheduler is to provide a balanced mix of jobs, such as I/O bound and processor bound.
  • It also controls the degree of multiprogramming.
  • If the degree of multiprogramming is stable, then the average rate of process creation must be equal to the average departure rate of processes leaving the system.
  • On some systems, the long term scheduler may not be available or minimal.
  • Time-sharing operating systems have no long term scheduler.
  • When the process changes the state from new to ready, then there is the use of long term scheduler.

Short Term Scheduler

  • It is also called CPU scheduler.
  • The main objective is increasing system performance in accordance with the chosen set of criteria.
  • It is the change of ready state to the running state of the process.
  • CPU scheduler selects process among the processes that are ready to execute and allocates CPU to one of them.
  • Short term scheduler also known as a dispatcher, execute most frequently and makes the fine-grained decision of which process to execute next.
  • Short term scheduler is faster than a long term scheduler.

Medium Term Scheduler

  • Medium term scheduling is part of the swapping
  • It removes the processes from the memory.
  • It reduces the degree of multiprogramming.
  • Running process may become suspended if it makes an I/O request.
  • Suspended processes cannot make any progress towards completion.
  • In this condition, to remove the process from memory and make space for other processes, the suspended process is a move to secondary storage.
  • This process is called swapping, and the process is said to be swapped out or rolled out.
  • Swapping may be necessary to improve the process mix of handling the swapped out-processes.




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