Question

What is the waiting time and Turnaround time of each process for each of the scheduling algorithms? [12 Marks]

Job

Arrival Time

Burst(msec)

Priority

A

0

6

3 (Silver)

B

1

2

1 (Diamond)

C

3

5

3 (Silver)

D

5

3

4 (Bronze)

E

7

2

2 (Gold)

(a) First-Come-First-Served (FCFS) scheduling [2 Marks]

(b) Preemptive PRIORITY scheduling [2 Marks]

(c) Highest Response Ratio Next (HRRN) scheduling [2 Marks]

(d) Round Robin (RR) (quantum = 4) scheduling [2 Marks]

(e) Which of the foregoing scheduling policies provides the lowest waiting time for this set of jobs? What is the waiting time with this policy? (Show your work) [4 Marks]

Answer 1

Question:

Process	AT	BT	Priority
A	0	6	3
B	1	2	1
C	3	5	3
D	5	3	4
E	7	2	2

a) FCFS

Process	AT	BT	Priority	TAT	WT
A	0	6	3	6	0
B	1	2	1	7	5
C	3	5	3	10	5
D	5	3	4	11	8
E	7	2	2	11	9

Turn Around Time: Time Difference between completion time and arrival time.
Turn Around Time = Completion Time – Arrival Time

Waiting Time(W.T): Time Difference between turn around time and burst time.
Waiting Time = Turn Around Time – Burst Time

Average Waiting Time = (0+5+5+8+9)/5 = 5.4

Please find Gantt Charts of all scheduling policies:

b) Preemtive Priority Scheduling:

Process	AT	BT	Priority	TAT	WT
A	0	6	3	10	4
B	1	2	1	2	0
C	3	5	3	12	7
D	5	3	4	13	10
E	7	2	2	2	0

Average Waiting Time = (4+0+7+10+0)/5 = 4.2

c) HRRN:

The name itself states that we need to find the response ratio of all available processes and select the one with the highest Response Ratio. A process once selected will run till completion.

Criteria – Response Ratio
Mode – Non-Preemptive

Response Ratio = (WT + BT)/BT

At t=6 conflict arises so calculate response ratio of B,C and D.

Response Ration (B) = (5+2)/2 = 3.5

Response Ration (C) = (3+5)/5 = 1.6

Response Ration (D) = (1+3)/3 = 1.33

So B will be selected.

At t=8 conflict arises so calculate response ratio of E,C and D.

Response Ration (E) = (1+2)/2 = 1.5

Response Ration (C) = (5+5)/5 = 2

Response Ration (D) = (3+3)/3 = 2

So C will be selected based on the arrival time as Respose Ration is same .

At t=13 conflict arises so calculate response ratio of E and D.

Response Ration (E) = (8+3)/3 = 3.66

Response Ration (D) = (6+2)/2 = 4

So D will be selected.

Process	AT	BT	Priority	TAT	WT
A	0	6	3	6	0
B	1	2	1	7	5
C	3	5	3	10	5
D	5	3	4	11	8
E	7	2	2	11	9

Average Waiting Time = (0+5+5+8+9)/5 = 5.4

d) RR with time quantum 4:

Process	AT	BT	Priority	TAT	WT
A	0	6	3	12	6
B	1	2	1	5	3
C	3	5	3	15	10
D	5	3	4	10	7
E	7	2	2	10	8

Average Waiting Time = (6+3+10+7+8)/5 = 6.8

e) Which of the foregoing scheduling policies provides the lowest waiting time for this set of jobs? What is the waiting time with this policy?

Preemtive Priority Scheduling has the lowest waiting times for the set of jobs. Average Waiting Time = (4+0+7+10+0)/5 = 4.2 which is lowest amingst all.