Question

##1, Assume that you have the following processes all arriving at time 0:

Process	Burst	Priority
P1	8	4
P2	6	1
P3	1	2
P4	9	2
P5	3	3

For each of the following CPU scheduling algorithms, determine the turnaround and wait times for each process as well as the average wait and turnaround times.

v First Come First Serve

v non-preemptive SJF

v preemptive SJF

v Non-Preemptive Priority Scheduling

v Round Robin (assume a quantum of 1)

Which of the four algorithms has the shortest wait time? Which has the fastest average turnaround time?

Answer 1

Turn around time = completion time - arrival time

Waiting time = turn around time - burst time

As arrival time is 0 fir all the processes, turn around time and completion time will be same for all the CPU scheduling types.

FCFS:

Process	Burst time	Completion time	Waiting time	Turn around time
P1	8	8	0	8
P2	6	14	8	14
P3	1	15	14	15
P4	9	24	15	24
P5	3	27	24	27

Non preemptive SJF:

Process	Burst time	Completion time	Waiting time	Turn around time
P1	8	18	10	18
P2	6	10	4	10
P3	1	1	0	1
P4	9	27	18	27
P5	3	4	1	4

Preemptive SJF:

Both non preemptive and preemptive SJF are same as the arrival time for all the processes are 0. Hence the process with shortest burst time will be processed at any time in both the scheduling types.

Process	Burst time	Completion time	Waiting time	Turn around time
P1	8	18	10	18
P2	6	10	4	10
P3	1	1	0	1
P4	9	27	18	27
P5	3	4	1	4

Non-preemptive priority based:

Process	Burst time	Completion time	Waiting time	Turn around time
P1	8	27	19	27
P2	6	6	0	6
P3	1	7	6	7
P4	9	16	7	16
P5	3	19	16	19

Round robin(qt : 1):

Process	Burst time	Completion time	Waiting time	Turn around time
P1	8	25	17	25
P2	6	21	15	21
P3	1	3	2	3
P4	9	27	18	27
P5	3	13	10	13

Thus

The shortest waiting time: 18

The algorithms that have shortest waiting time are:

Non preemptive SJF, preemptive SJF and round robin

Average turn around time for fcfs:

(8+14+15+24+27)/5=88/5=17.6

Average turn around time for non preemptive SJF & preemptive SJF:

(18+10+1+4+27)/5=60/5=12

Average turn around time for non-preemptive priority based:

(27+6+7+19+16)/5=75/5=15

Average turn around time for Round robin:

(25+27+3+21+13)/5=89/5=17.8

Fast average turnaround time is for: Non-preemptive and preemptive SJF