Question

For the processes listed in the following table, which of the following scheduling schemes will give the lowest average turnaround time?

Process	Arrival Time	Processing Time
A	0	3
B	1	6
C	4	4
D	6	2

1. First come First Serve
2. Non-peemptive Shortest Job First
3. Shortest Remaining Time
4. Round Robin with Quantum value two

Answer 1

Correct Answer - Option 3 : Shortest Remaining Time

Scheduling Algorithm:

First come first serve

Gantt chart:

A

B

C

D

0                 3                  9                 13               15

Process Table:

Process	Arrival Time	Processing Time	Completion time	Turnaround time
A	0	3	3	3
B	1	6	9	8
C	4	4	13	9
D	6	2	15	9

 

Average turnaround time = 29/4 = 7.25

Scheduling Algorithm:

Non pre-emptive shortest job first

Gantt chart:

A

B

D

C

0            3             9            11           15

Process Table:

Process	Arrival Time	Processing Time	Completion time	Turnaround time
A	0	3	3	3
B	1	6	9	8
C	4	4	15	11
D	6	2	11	5

 

Average turnaround time = 27/4 = 6. 75

Scheduling Algorithm:

Shortest remaining time first

Gantt chart:

A

B

C

D

B

0           3            4            8           10         15

Process Table:

Process	Arrival Time	Processing Time	Completion time	Turn around time
A	0	3	3	3
B	1	6	15	14
C	4	4	8	4
D	6	2	10	4

 

Average turnaround time = 25/4 = 6.25

Scheduling Algorithm:

Round Robin with Quantum value two

Gantt chart:

A

B

A

C

B

D

C

B

0       2       4        5       7        9       11     13     15

Process Table:

Process	Arrival Time	Processing Time	Completion time	Turnaround time
A	0	3	5	5
B	1	6	15	14
C	4	4	13	9
D	6	2	11	5

 

Average turnaround time = 33/4 = 8.25

So, shortest remaining time first has the minimum average turnaround time.