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Which of the following scheduling algorithms is non-preemptive?

1. Round Robin
2. First-In First-Out
3. Multilevel Queue Scheduling
4. Multilevel Queue Scheduling with Feedback

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1. Here we preempt when Time quantum is expired.

2. We never preempt, so answer is (B) FIFO

3. Here we preempt when process of higher priority arrives.

4. Here we preempt when process of higher priority arrives or when time slice of higher level finishes & we need to move process to lower priority.

Your answer is obviously correct. However, can you give me a source for your reasoning for options C and D.

Galvin (8th ed) only says that the multilevel and multilevel feedback algorithms have an independent  scheduling algorithm for each queue, but dont specify when preemtion occurs.
Sir what does it mean by"when time slice of higher level finishes & we need to move process to lower priority."
@ rajinder singh

consider you have 3  queue  like A,B,C & each queue has own time slice 5,8,10 respectively

suppose  process P1 is executing in Queue B .but  B Queue time slice expired before finish Time slice of P1 . then you have to shift P1 process to  C Queue .
ans is b

### 1 comment

FCFS - non-preemptive

Round robin -  preemptive

Multilevel Queue Scheduling - preemptive

Multilevel Queue Scheduling with Feedback - preemptive

SJF - non-preemptive

SRTF - preemptive

LRTF - preemptive

Highest Response ratio first - non-preemptive
Multi level Queue Scheduling can be both Preemptive and non preemptive depending on whether FCFS like algo’s are on the top level or not.

Generally, we dont place FIFO/FCFS on top level, so saying 100% surely that MLQ scheduling is non preemptive wont be a fair thing

But FCFS or FIFO in process scheduling is definately non preemptive, and hence it causes starvation.

So definately FCFS/FIFO is the right answer.

PS: FCFS in disk scheduling, does not cause starvation.
by
NON PREEMPTIVE  PROPERY FOLLOW ONLY FCFS

BCZ ONCE YOU GIVE CPU TO PROCEES WE DOES TAKE UNTIL IS FINISH THE WORK SO THAT WHY NON PREEMPTIVE IS ONLY OPTION IS FCFS