What is the difference between pre emptive and non preemptive scheduling?

Answer 1

in pre emptive scheduling. a limited time period is fixed for every process in the CPU. no matter whether the process is completed or not ... the resource assinged to it will be taken back back abd will be given to the next process in the queue.

while in non preemptive the resorces are with a process untill it finishes completely others wait for their turn till then. this kind of scheduling has a high probability of going into a deadlock.

Answer 2

Tasks are usually assigned with priorities. At times it is necessary to run a certain task that has a higher priority before another task although it is running. Therefore, the running task is interrupted for some time and resumed later when the priority task has finished its execution. This is called preemptive scheduling.

Eg: Round robin

In non-preemptive scheduling, a running task is executed till completion. It cannot be interrupted.

Eg First In First Out

Answer 3

• Non-Preemptive: Non-preemptive algorithms are designed so that once a process enters the running state(is allowed a process), it is not removed from the processor until it has completed its service time ( or it explicitly yields the processor).

  context_switch() is called only when the process terminates or blocks.

• Preemptive: Preemptive algorithms are driven by the notion of prioritized computation. The process with the highest priority should always be the one currently using the processor. If a process is currently using the processor and a new process with a higher priority enters, the ready list, the process on the processor should be removed and returned to the ready list until it is once again the highest-priority process in the system.

  context_switch() is called even when the process is running usually done via a timer interrupt.

Answer 4

In preemptive scheduling, a process that is being allotted processor is forcely removed and the processor is given to some other process.

In non-preemptive scheduling, there are no forcible removals.

FCFS,SJF are non-preemptive.

Round Robin is preemptive

Answer 5

On a preemptive kernel, a process running in kernel mode can be replaced by another process while in the middle of a kernel function.

On a nonpreemptive kernel, process A would just have used all the processor time until he is finished or voluntarily decides to allow other processes to interrupt him (a planned process switch).

Answer 6

In preemptive scheduling we preempt the currently executing process.

In non preemptive we allow the current process to finish its CPU burst time.