Question

The following table lists the characteristics of three processes that require service in a time-sharing system Assume that no time is required to choose the next process and perform a context switch. For each algorithm, show the process that is running in each time interval

Process Name	Arrival Time	Burst/CPU Time	Priority	Start Time	End Time	Turnaround (TA) Time	WTA	Wait
P1	2	8	1
P2	4	5	4
P3	6	2	3

p4

3

4

2

d) Preemptive Shortest Job First (Shortest Remaining Time First (SRTF))

Time	0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21
Process

d) Priority Scheduling (PRI): Preemptive

Time	0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21
Process

d) Round Robin: Time Quantum =2, context switch =1.

Time	0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21
Process

Answer 1

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Process Name	Arrival Time	Burst Time	Priority
P1	2	8	1
P2	4	5	4
P3	6	2	3
P4	3	4	2

A.) Shortest Remaining Time First(Shortest Job first that is Preemptive) :-

1. This first process Comes at Time 2. So, till then, the CPU is empty.

2. Now P1 arrives and has Shortest Remaining time of 8 seconds. So, it goes at time=2

3. However at time = 3, P4 arrives and preempts P1. P1 now has 7 seconds left. P4 enters CPU at t=3

4. When P2 enter at t=4, P4 has remaining 3 seconds and so P2 waits at it has burst time of 5.

5. At t=6, P3 enters and sees that it has burst time of 2, but P4 has only 1 second left. So, it waits 1 second.

6. At t=7, P3 enters with shortest burst time. At t=8, P2 enters with burst time of 5. At t=14, P1 enters.

T	0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21
P	-	-	P1	P4	P4	P4	P4	P3	P3	P2	P2	P2	P2	P2	P1	P1	P1	P1	P1	P1	P1	-

B.) Priority Scheduling Preemtive :-

1. This first process Comes at Time 2. So, till then, the CPU is empty.

2. Now P1 arrives and is only process so enters. It has priority 1 which is highest and so first completes and leaves at t=9. rest processes arrive and wait.

3. Next according to priority is P4, then P3 and then P2

T	0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21
P	-	-	P1	P1	P1	P1	P1	P1	P1	P1	P4	P4	P4	P4	P3	P3	P2	P2	P2	P2	P2	-

C.) Round Robin. Time Quantum = 2.

Job is changed every 2 seconds,

1. P1 executes for 2 seconds. Now at t=4, there are P4 and P2. P4 enters then P2. At t=6, P3 has joined.

Then robin goes like P1[6],P4[2],P2[3].

P1[4], P2[1]

P1[2]

T	0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21
P	-	-	P1	P1	P4	P4	P2	P2	P3	P3	P1	P1	P4	P4	P2	P2	P1	P1	P2	P1	P1	-