Difference Between Preemptive and Non Preemptive Scheduling in Operating Systems

Preemptive Scheduling is a CPU scheduling procedure that works by separating time allotments of CPU to a given interaction.

Whereas Non-Preemptive Scheduling is a CPU scheduling procedure in which the cycle takes the asset (CPU time) and holds it till the interaction gets ended or is pushed to the holding upstate.

There is a cost associated with the Preemptive process, while in the Non-Preemptive process, there is no cost.

Preemptive vs Non-Preemptive Scheduling

The main difference between Preemptive and Non-Preemptive Scheduling is that in Preemptive Scheduling, we can plan the operations, and they can be scheduled easily. On the other hand, in Non-Preemptive Scheduling, the operation that is being performed cannot be scheduled. The process can be interrupted while it is not possible in Non-Preemptive.

Preemptive vs Non Preemptive Scheduling

Preemptive Scheduling is basically a strategy where the operations are generally allocated with their needs.

It is utilized when a cycle changes from running state to prepared state or holding from the prepared state. In Preemptive Scheduling, the operation can be interrupted easily.

In the Non-Preemptive Scheduling, the CPU has been assigned to a particular interaction. The operation that is assigned to the CPU has to be finished to move on to the next operation.

The only technique that can be utilized for different hardware stages. Non-Preemptive Scheduling happens when an operator enters the stand-by state or ends.

Comparison Table Between Preemptive and Non-Preemptive Scheduling in Operating Systems

 Parameters of ComparisonPreemptive SchedulingNon-preemptive Scheduling
Flexibility It is flexible. It is non-flexible.
Cost It is cost-associated. It is non-cost associated.
Algorithm It has an algorithm of overhead switching. It has no such algorithm for overhead switching.
Interruption The process can be interrupted easily.The process cannot be interrupted.
CPU utilization More efficient Less efficient

What is Preemptive Scheduling?

It is the function of the CPU scheduler to distribute a cycle to the CPU at whatever point the CPU is in the inactive state. The CPU scheduler chooses a cycle from the prepared line and assigns the interaction to the CPU.

In this kind of planning, the assets (CPU Cycle) have been designated to operate for a restricted measure of time. An operation can be interrupted when it is being performed or executed.

In preplanned planning, in the event that a cycle that has a high need shows up in the prepared line, the operation which has a low need gets stopped, and let’s finish the operation with high need.

Assuming on the off chance that a cycle that has the most noteworthy need shows up, this operation doesn’t hold for the whole operation to finish.

Rather than what it will do, it will interrupt the cycle and make the process steady, and it will start the operation for that process which has high priority.

This allows the cycle to get finished, which has higher priority than the other, and once the operation is over, it will start the next one.

Hence along these lines, every one of the operations which are in the accessible line gets an ideal opportunity to run.

What is Non-Preemptive Scheduling?

The operation which happens when a process ends or changes from ongoing to waiting for state this sort of CPU operation is called Non-Preemptive Scheduling.

This type of scheduling is applied when the operations are finished from one state to the other.

In this type of process, it does not have the function to interrupt the operation like in Preemptive one, so what happens is once the process is started, it will be finished without any interruption.

It is generally because, in Non- Preemptive Scheduling, it does not have the function to interrupt the operation in between, due to which it has to wait once the first operation is finished.

All things considered, it holds up till the cycle finishes its operation, and then once it is over, it will be transferred to the other operation. 

The only strategy that can be utilized for different hardware stages. That is on the grounds that it needs specific equipment like precautionary Scheduling.

In Non-Preemptive Scheduling, there is no such algorithm for switching overhead operation due to which CPU has to wait until the next operation is transferred.

As it cannot be interrupted, therefore which makes the Non-preemptive Scheduling as in-flexible as compared to Preemptive Scheduling

Main Differences Between Preemptive and Non-Preemptive Scheduling in Operating Systems

  1. In Preemptive Scheduling, the process can be interrupted easily, while in Non-Preemptive Scheduling, the cycle which is going on it has to be finished first to move on to the next cycle.
  2. In Preemptive Scheduling, the process has an overhead as it has to schedule multiple operations, while in Non-Preemptive Scheduling, there is nothing like that because it doesn’t provide any function for the interruption in between the process.
  3. Preemptive Scheduling is flexible(i.e., can be easily altered) in nature compared to Non-Preemptive Scheduling, which is not.
  4. In Preemptive Scheduling, the process which has the higher priority is given first, while in the case of Non-Preemptive Scheduling, the operation which is going on has to be finished to move on to the next one.
  5. Preemptive Scheduling is cost-effective to run the operation you need to pay, while in the case of Non-Preemptive Scheduling, it is totally cost-free.


In Preemptive Scheduling, the operating system has the function to interrupt the cycles/operation that is being performed. This is generally because the operations which are having a higher priority are given the first.

Therefore, once the operation which is having a higher priority is performed, the previous operation has to starve, i.e., it has to wait until the current operation is finished.

It has an algorithm for overhead switching between the tasks assigned, while in the Non-Preemptive, it doesn’t have any such algorithms. 

Due to this, Preemptive Scheduling is flexible in nature and has a higher rate of efficiency as compared to Non-Preemptive Scheduling.

In Non-Preemptive Scheduling, once the cycle is started, the operator has to wait until the next cycle to be started. This is because it doesn’t support the feature of interruption in between the process.

Due to this, Non-Preemptive Scheduling is generally in-flexible and has a low-efficiency output.

The cost associated with Preemptive Scheduling is higher as compared to Non-Preemptive Scheduling, which is cost-free.

As the Preemptive Scheduling has the option to give priority to the higher task, due to which it takes more time to complete the task, whereas when we talk about the Non- Preemptive one, it will take less time as there is no intervention in between the process.


  1. https://hal.inria.fr/inria-00073732/
  2. http://clweb.csa.iisc.ernet.in/sarojini/rts/periodid-sporadic.pdf
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