FCFS least waiting time

Question

Answer 1

Both FCFS and SRTF gives the same Gantt chart.

A

B

C

D

E

0                        3                        7                            10                         15                      22  

Avg Waiting time = (0 + (3-3) + (7-7) + (10-9) + (15-12))/5 = 4/5  = 0.8 msec.

The Gantt chart for RR:

A

B

C

D

E

B

D

E

E

0             3          6   7            10            13          16           17            19          22          23

Avg Waiting time = (0 + [(3-3)+(16-6)] + (7-7) + [(10-9)+(17-13)] + [(13-12)+(19-16)] )/5 = (10+5+4)/5 = 19/5 = 3.8 msec.

Hence option D.

Comments

B will execute till 7 as there was no process in the system for that 1 sec