Preemptive vs Non Preemptive Scheduling in Operating Systems: Difference and Comparison

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.

Key Takeaways

1. Preemptive scheduling allows the operating system to forcibly interrupt a running process, while non-preemptive scheduling requires the process to relinquish control voluntarily.
2. Preemptive scheduling provides better response times and resource utilization than non-preemptive scheduling.
3. Non-preemptive scheduling is simpler but may result in less efficient system performance than preemptive scheduling.

Preemptive vs Non-Preemptive Scheduling

Preemptive scheduling allows higher-priority tasks to interrupt lower-priority ones, while non-preemptive scheduling does not. It is used in real-time systems, while non-preemptive scheduling is simpler and more predictable but may result in longer wait times for certain tasks.

Preemptive Scheduling is basically a strategy where the operations are 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

Parameters of Comparison	Preemptive Scheduling	Non-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 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.

References

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

Last Updated : 13 July, 2023