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In round robin CPU scheduling as time quantum is increased the average turn around time

  1. increases
  2. decreases
  3. remains constant
  4. varies irregularly
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4 Answers

Best answer
11 votes
11 votes

Ans - Decrease and Increase Both.

Example for decrease in the average turn round time :

 Suppose we have two process P1 and P2 with burst time  20 sec and 2 sec respectively. P1 arrives at time t= 0 sec and P2 at t=2 sec.

When time quantum for RR = 1 sec.

Then  TAT for P1 = 22 sec. and for P2 = 3 sec.

So AVG TAT = (22 + 3 ) /2 sec

Now do same with time quantum for RR = 2 sec.

You will get AVG TAT = (22 + 2 )/2 sec.


Example for increase in the average turn round time :

 Suppose we have two process P1 and P2 with burst time  20 sec and 5 sec respectively. P1 arrives at time t= 0 sec and P2 at t=5 sec.

When time quantum for RR = 5 sec.

Then  TAT for P1 = 25 sec. and for P2 = 5 sec.

So AVG TAT = (25 + 5 ) /2 sec. 

Now do same with time quantum for RR = 6 sec.

You will get AVG TAT = (25 +  6 )/2 sec.

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There are few criteria used for measuring the performance of a particular scheduling algorithm.

The turn around time is the interval of time between the submission of a process and its completion. 

The wait time is the amount of time a process has been waiting in the ready queue.

The response time is the time taken between the process submission and the first response produced.

In RR algorithm, the value of time quantum or the time slice, plays a crucial role in deciding how effective the algorithm is. If the time quantum is too small, there could be lot of context switching happening which could slow down the performance. If the time quantum is too high, then RR behaves like FCFS. If the time quantum is increased, the average response time varies irregularly. Hence average turn around time may be increased or decreased, it's totally depend on the situation. If you take any comprehensive material on operating system, you will come across a graph which depicts this behavior. 

1 votes
1 votes

In RR algorithm, the value of time quantum or the time slice, plays a crucial role in deciding how effective the algorithm is. If the time quantum is too small, there could be lot of context switching happening which could slow down the performance. If the time quantum is too high, then RR behaves like FCFS. If the time quantum is increased, the average response time varies irregularly.

Hence Option(D)Varies irregularly.

–1 votes
–1 votes
if time quantum will increase then waiting time(WT) in system will increase for other processes...as time quantum is large so burst time(BT) will also increase and

we know turn around time = WT + BT or CT-AT(completion time - arrival time)

I think TAT will also increase

answer should be  (c)
Answer:

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