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Types of Process Schedulers in OS

An OS operation called process scheduling arranges processes in various stages, such as ready, waiting, and running. An OS can assign a period of time for each process’s CPU execution through process scheduling. The fact that a process scheduling mechanism keeps the CPU active at all times is another crucial benefit. You may do this to get programs to respond as quickly as possible.

Type of Process Schedulers

A form of system software called a scheduler enables you to manage process scheduling.
There are mainly three types of Process Schedulers:

  1. Long Term Scheduler
  2. Short Term Scheduler
  3. Medium Term Scheduler

What is Long Term Scheduler in OS?

Bringing processes from the JOB queue (or secondary memory) into the READY queue is the job of a long-term scheduler (or main memory). In other words, a long-term scheduler decides which applications will be loaded into Memory for CPU processing.

Job schedulers are another name for long-term schedulers. The effectiveness of the CPU is affected over the long term by long-term schedulers. They are in charge of handling all of the processes in the READY queue and the degree of multiprogramming.

A long-term scheduler is removed from some operating systems. Examples of time-sharing operating systems without a long-term scheduler include Windows and UNIX. For the short-term scheduler, these systems place all the processes in the main memory.

What is the Function of a Long Term Scheduler?

A long-term scheduler’s primary purpose is to balance CPU bound jobs, those where the CPU takes up the majority of processing time and I/O bound jobs, those where the I/O operations take up the majority of processing time in order to reduce processing time.

In order for the average rate at which a process enters the system to be equal to the average rate at which a process exits, long-term schedulers must maintain a certain level of multiprogramming. As executions take a while to complete, the long-term schedulers have plenty of time to choose which processes to place in the queue.

Example of a Long Term Scheduler in OS

Imagine an I/O-bound long-term scheduler that generates all processes. In this scenario, we won’t be making the most use of our CPU because it will be idle for the majority of the time. On the other hand, if a long-term scheduler launches all CPU-bound processes, the CPU will be busy for a considerable amount of time, the devices will be idle for the majority of the time, and the I/O waiting for queue will be idle.

We won’t be using our technology to its full capacity in these instances. But, if the long-term scheduler designs processes with the ideal ratio of CPU- and I/O-bound workloads, we will be fully using the system and cutting down on process time.

What is a Short-Term Scheduler?

A CPU Scheduler is another name for the short-term scheduler. The primary responsibility of the short-term scheduler is to choose a ready-to-run task from the Ready Queue and allocate a processor to it. Short-term Scheduler execution is more common than long-term Scheduler execution. In terms of the Multiprogramming Degree, it has less control. The bare minimum accessible in the Time-Sharing System is the short-term scheduler.

Main Differences between the Long Term Scheduler and Short Term Scheduler

The key differences between the short-term and long-term schedulers are explained here. The following are some of the differences between the long-term scheduler and the short-term scheduler:

  1. An operating system scheduler known as a long-term scheduler selects tasks from the work queue and loads them for execution in main memory. A short-term scheduler, on the other hand, is an operating system scheduler that selects the process from among the many that the CPU executes.
  2. The processes or jobs are selected by the long-term scheduler from the job pool. The short-term scheduler, on the other hand, picks the processes from the ready queue.
  3. The degree of multiprogramming is controlled by the long-term scheduler. The short-term scheduler, on the other hand, has less control over multiprogramming.
  4. The work is assigned by the long-term scheduler to the ready queue for further processing by the short-term scheduler, also known as a job scheduler. Instead, the short-term scheduler, also known as a CPU scheduler, allocates the job to the CPU for its process.
  5. Compared to the long-term scheduler, the short-term scheduler selects processes from the ready queue more often.
  6. Short-term scheduling is quicker than long-term scheduling.


  • Processes from the JOB queue (secondary memory) are transferred into the READY queue by long-term schedulers (main memory).
  • A job scheduler is another name for a long-term scheduler.
  • Long-term schedulers are not present in all operating systems.
  • A long-term scheduler’s primary function is to maintain a balance between the workloads that are CPU and I/O bound in the main memory.

FAQs Related to Long Term Schedular in OS

1. What are the three types of Scheduler in OS?
Process scheduler in OS is divided into three types:

  • Long term scheduler in OS
  • Mid term scheduler in OS
  • Short tern scheduler in OS

2. What is the advantage of long term scheduler in OS?
Scheduling for the long term serves as a gatekeeper. It determines if the system has adequate memory or space to accept new programs or jobs. It restricts multitasking to avoid affecting presently running processes negatively.

3. What are the types of scheduling in OS?
Scheduling types in OS are as follows:

  • First-Come, First-Served (FCFS) Scheduling.
  • Shortest-Job-Next (SJN) Scheduling.
  • Priority Scheduling.
  • Shortest Remaining Time.
  • Round Robin(RR) Scheduling.
  • Multiple-Level Queues Scheduling.

4. Which scheduler is faster?
CPU scheduler is another name for a short-term scheduler. Long term is slower than short term in terms of pace. Between short- and long-term schedulers, medium-term schedulers operate at a pace. Of the other two, short term moves with the greatest pace.

5. What is the difference between long term, mid term, and short term scheduler in OS?
The condition of the long-term scheduler process is (New to Ready). The scheduling process status at this moment is (Ready to Running). Processes are chosen from the pool and uploaded into memory for execution by the long-term scheduler. Processes can be reinstated in the medium term scheduler and their execution can continue.

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