An Operating System has many tasks lined up every minute. It is indeed designed to connect all the programs and execute on task offer. Process Scheduling is an important task for an Operating System. The Operating System Processes different tasks in different states; ready, running, and waiting.
The important reason for process scheduling is it allows the operating system to allocate certain time intervals of the processor for every process. The main task of process scheduling is to keep the processor working all the time seamlessly to experience minimum wait time for all the programs.
There are three processes states: Running, Waiting, and Ready. Process scheduling has different queues for different states. All the tasks with similar states are directed to the same queue. If any of the tasks’ state is changed, it shifts to the corresponding queue.
There are three categories of queues available for process scheduling. They are job queue, ready queue, and device queue. The processes of the system are stored in the job queue. Ready queue lines up all the tasks that are waiting to be executed while Device queue takes care of the peripherals and internal system devices.
Short Term vs Long Term Scheduler
The main difference between a Short term Scheduler and a Long-term Scheduler is how the task is executed. Short Term Scheduler facilitates the selection of process from the Ready Queue and allocates it to the processor for execution, while Long term scheduler helps to select the process from the job pool and allocate in the ready queue.
Two types are schedulers work in tandem to facilitate process scheduling Short term and Long-term Schedulers are the system software that handles the process scheduling effectively.
Comparison Table Between Short Term and Long Term Scheduler (in Tabular Form)
|Parameter of Comparison||Short – Term Scheduler||Long-Term Scheduler|
|Task||It selects the process from the Ready queue to send it to the CPU.||The process is selected from the job pool passes it on to the ready queue.|
|Frequency||The frequency of short term scheduling is more.||Long term scheduler is not as frequent as the short-term in scheduling the process.|
|Control of Multi-Programming||Short-term Scheduler has less control over multi-programming.||Long-term Scheduler has control over the multi-programming.|
|Time-Sharing System||Short- term Scheduler has its minimal presence in a time-sharing system.||The long-term scheduler is not available in the time-sharing system.|
|Name Alternative||It is otherwise called as CPU Scheduler.||It is otherwise called as Job Scheduler.|
What is Short Term Scheduler?
Short term Scheduler is system software that selects the processes from the ready queue and sends it to the Processor for its execution. Short term Scheduler is otherwise called as CPU Scheduler.
In the time-sharing system, Short term scheduler is minimally present. The short-term scheduler’s execution happens often and also more frequent than the long-term scheduler.
The degree of multiprogramming is also limited and has less control over it. Short term scheduler uses an algorithm that decides which process shall be scheduled for execution.
The execution of the processes takes a few milliseconds and this is one of the reasons why it is more frequent than the long-term scheduler. The algorithm which decides the processes to be selected is of prime importance as it decides which one to go next.
The process with long waiting time must be selected from the ready queue. That means to say once a process is selected, all the other processes shall wait for its turn.
If the short-term scheduler makes a mistake in choosing a process that has long burst time, there will be an error which is called starvation.
Starvation is a short-term scheduler’s fault in taking the correct process into execution. This can be observed in delay in file opening, delay in opening a program asked for.
What is Long Term Scheduler?
Long term scheduler is system software that selects the process from the job pool and ejects it to the ready queue for further process by the short-term scheduler. There are many instances where many programs are submitted for execution, and many times, executing all the tasks immediately is not possible.
These tasks are stored in a pool called the job pool. The tasks shall be waiting for its turn while the long-term scheduler selects the process with a long wait time and send it to the ready queue for its execution.
Long term scheduler is otherwise called as a Job scheduler. The frequency of the long-term scheduler’s process is less when compared to the short-term scheduler.
Unlike the short-term scheduler, the long-term scheduler manages multi-program in a versatile fashion. It is the one that separates the programs as per the timeline and feeds it to the ready queue.
Long term scheduler has a greater responsibility in selecting the processes keeping the Input/ Output and the processor bound tasks in line. This ensures optimum system throughput and proper functionality too.
It is to be understood that the main task of the long-term scheduler is to provide mixed jobs to the ready queue. This is further selected by the short-term scheduler for its execution.
Main Differences Between Short Term and Long Term Scheduler
- The main difference between Short-term Scheduler and Long Term Scheduler is, the short-term scheduler selects the processes from the ready queue one by one and feeds it to the CPU for further execution while Long-term scheduler selects the processes from the mass storage of tasks called job pool and sends it to the ready queue.
- Short-term Scheduler is more frequent in selecting the processes from the ready queue than the long-term scheduler from the job pool.
- Short-term scheduler has less control over multi-programming whereas Long-term scheduler controls the degree of multi-programming.
- The short-term scheduler is minimally present in the time-sharing system whereas long-term scheduler is not present in the time-sharing system.
- The short-term scheduler allocates the task to the CPU for its process so it is also called as CPU scheduler whereas the Long-term scheduler allocates the task to ready queue for further action by the short-term scheduler, it is called as a job scheduler.
The process scheduling has an important objective of balancing the response and utilization. This shall maximize the number of users by offering minimum wait time for the programs to process. The scheduling shall happen in tandem and it must not miss on the timeline.
The functionality of the long term and the short-term scheduler is critical to have the system function seamlessly. If there is an error in execution, it could be easily identified if the short-term schedule is at fault or the long terms scheduler. Most of the time, the system may be sluggish on offering a variety of commands for the CPU to process.
However, it is to be noted that, to reach the CPU, it must go through the selection process of Short term and Long-term scheduler.