Premptive Scheduling Vs Non-premptive Scheduling

The scheduling which takes place when a process switches from running state to ready state or from waiting state to ready state is called Preemptive Scheduling. On the hands, the scheduling which takes place when a process terminates or switches from running to waiting for state this kind of CPU scheduling is called Non-Preemptive Scheduling. The basic difference between preemptive and non-preemptive scheduling lies in their name itself. That is a Preemptive scheduling can be preempted; the processes can be scheduled. In Non-preemptive scheduling, the processes can not be scheduled.

Key Differences Between Preemptive and Non-Preemptive Scheduling:

  1. The basic difference between preemptive and non-preemptive scheduling is that in preemptive scheduling the CPU is allocated to the processes for the limited time. While in Non-preemptive scheduling, the CPU is allocated to the process till it terminates or switches to waiting state.
  2. The executing process in preemptive scheduling is interrupted in the middle of execution whereas, the executing process in non-preemptive scheduling is not interrupted in the middle of execution.
  3. Preemptive Scheduling has the overhead of switching the process from ready state to running state, vise-verse, and maintaining the ready queue. On the other hands, non-preemptive scheduling has no overhead of switching the process from running state to ready state.
  4. In preemptive scheduling, if a process with high priority frequently arrives in the ready queue then the process with low priority have to wait for a long, and it may have to starve. On the other hands, in the non-preemptive scheduling, if CPU is allocated to the process with larger burst time then the processes with small burst time may have to starve.
  5. Preemptive scheduling is quite flexible because the critical processes are allowed to access CPU as they arrive into the ready queue, no matter what process is executing currently. Non-preemptive scheduling is rigid as even if a critical process enters the ready queue the process running CPU is not disturbed.
  6. The Preemptive Scheduling is cost associative as it has to maintain the integrity of shared data which is not the case with Non-preemptive Scheduling.

Conclusion:

It is not that preemptive scheduling is better than non-preemptive scheduling or vise-verse. All depends on how a scheduling minimizes the average waiting time of the processes and maximizes CPU utilization.

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