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:
- Long Term Scheduler
- Short Term Scheduler
- 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.
|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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