The Gateway to Computer Science Excellence
0 votes
998 views
What happens to average Turn Around Time if time quantum increased?
in Operating System by Active (4.4k points) | 998 views

2 Answers

+1 vote
Best answer

Turn around time (TAT) = Completion Time - Arrival Time

Round Robin = Process Burst Time / Time Quantum = Number of times a process is scheduled.

Which means, more the Time Quantum, lesser number of times the process would be scheduled

and less the Time Quantum, more number of times the process would be scheduled.

More the number of times the process is scheduled, more will be its Completion Time.

Keeping Arrival Time constant, more the Completion Time, more will be the Turn Around Time (TAT)

So, if a time Quantum is increased, 

  • Number of times a process is scheduled will increase
  • So, it Completion Time will increase
  • Thus its Turn Around Time would increase

** Please note: Keeping Arrival Time constant

by Loyal (5.5k points)
selected by
+1
final conclusion is wrong..
it should be:
more the Time Quantum, lesser number of times the process would be scheduled
and hence completion time will decrease resulting in decrement of TAT.
therefore avg. TAT will decrease on inc of time quantum
0
Yes, I agree the final conclusion is wrong. To quote "too_simple"

it should be:
more the Time Quantum, lesser number of times the process would be scheduled
and hence completion time will decrease resulting in decrement of TAT.
therefore avg. TAT will decrease on inc of time quantum
0
Well, your conclusion is also wrong.

On increasing the time quantum, TAT may increase or may decrease.
0
Well now I come to think of it,

The number of times the process wil scheduled will either remain same or it will decrease, it will NEVER increase. However, the turn around time may increase of decrease given the scheduling pattern.

Case where it might increase

Initially time quanta 2

P1 needs 7 time quanta to finish and P2 and P3 needs 10. All arrives at 0

P1(2) P2(2) P3(2), P1(2) P2(2) P3(2), P1(2) P2(2) P3(2), P1(1), P2(2), P3(2), P2(2) P3(2)

TAT for P1= 19, P2 = 25, P3 = 27

Avg TAT = 23.6667

Increase the time quanta to 3

P1(3) P2(3) P3(3), P1(3) P2(3) P3(3), P1(1) P2(3) P3(3), P2(1), P3(1)

TAT for P1: 19, P2 = 26, P3 = 27

Avg TAT = 24
0
Exactly !
0 votes
Rewriting my comment as answer:

If we increase the time quantum alloted to each process, the number of times the process will be scheduled will either remain same or it will decrease, it will NEVER increase. However, the turn around time may increase of decrease given the scheduling pattern.

Its easy to see where this will decrease. Case where it will increase:
===============================
Initially time quanta 2

P1 needs 7 time quanta to finish and P2 and P3 needs 10. All arrives at 0

P1(2) P2(2) P3(2), P1(2) P2(2) P3(2), P1(2) P2(2) P3(2), P1(1), P2(2), P3(2), P2(2) P3(2)

TAT for P1= 19, P2 = 25, P3 = 27

Avg TAT = 23.6667
--------------------------------------------------
Increase the time quanta to 3

P1(3) P2(3) P3(3), P1(3) P2(3) P3(3), P1(1) P2(3) P3(3), P2(1), P3(1)

TAT for P1: 19, P2 = 26, P3 = 27

Avg TAT = 24

===================
by Active (3k points)

Related questions

Quick search syntax
tags tag:apple
author user:martin
title title:apple
content content:apple
exclude -tag:apple
force match +apple
views views:100
score score:10
answers answers:2
is accepted isaccepted:true
is closed isclosed:true
50,737 questions
57,292 answers
198,236 comments
104,919 users