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Difference between Long-Term and Short-Term Scheduler
In the context of computer systems, a program or task in execution is called a process. In modern computers, several types of processes are used. The process of selecting one process from a bunch of processes and assigning it to the processor for execution is referred to as scheduling. The component of the system that accomplish this task is called a scheduler. There are two main types of schedulers, namely, Long−Term Scheduler and Short−Term Scheduler.
In this article, we will discuss the important differences between long−term scheduler and short−term scheduler. But before that, let's start with some basics of long−term and short−term schedulers so that it becomes easier to understand their difference.
What is a Long Term Scheduler?
Long term schedulers are also termed as Job schedulers. It maintains a queue of programs/jobs which are selected for system to process. Programs are selected based on the scheduling mechanism and processed. Long term schedulers control the degree of multiprogramming.
In a long−term scheduler, various processes wait for execution on the computer system in a job queue. The long−term scheduler picks a job from the job queue and brings that job to the ready queue to execute.
What is a Short Term Scheduler?
Short term schedulers are also termed as CPU schedulers. It maintains a context switch and CPU is switched among multiple threads. Short terms schedulers control the degree of multitasking. A short−term scheduler picks a job from the ready queue and assigns the CPU to it. A short−term scheduler has less control over the degree of multiprogramming. The execution of a short−term scheduler is frequent which means it selects the processes from the ready queue more frequently. Therefore, the short−term scheduler is relatively faster.
Difference between Long−Term Scheduler and Short−Term Scheduler
The following table highlights some of the important differences between a long term scheduler and a short term scheduler:
Key |
Long Term Scheduler |
Short term Scheduler |
---|---|---|
Input |
Long term schedulers take jobs from a job pool and manage them. |
Short term schedulers take processes from a ready queue and context switch the CPU. |
Known as |
Long term schedulers are known as Job Scheduler. |
Short term schedulers are known as CPU schedulers. |
Queue |
A queue of job is maintained as a job pool. The scheduler decides which job to pick. |
No such queue is present. |
Regulates |
Long term schedulers control Multiprogramming. |
Short term schedulers control multitasking. |
Priority |
Long term schedulers prioritize the programs to be selected for processing based on the provided mechanism. |
Short term schedulers set the importance of processes based on operation type. |
Speed |
Long term schedulers are slower. |
Short term schedulers are faster. |
Process selection |
Long term schedulers select processes from the job pool. |
Short term schedulers select processes from the ready queue. |
Job assignment |
Long term schedulers assign a job to the ready queue. |
Short term schedulers assign a job to the CPU for execution. |
Conclusion
Both long−term and short−term schedulers are necessary for scheduling the processes in a computer system. The most significant difference between the two is that a long−term scheduler picks a job from the memory and assigns it to the ready queue, while a short−term scheduler selects the job from the ready queue and assigns it to the CPU for its processing.