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Consider the following set of processes, assuming all are arriving at time 0.
written 6.8 years ago by gravatar for teamques10 teamques10 ★ 70k •   modified 4.2 years ago
Process Burst Time Priority
P1 2 2
P2 1 1
P3 8 4
P4 4 5
P5 5 3

Calculate average waiting time and turn-around time for FCFS, SJF (Non-Pre-emptive), Priority and RR (Quantum=2).

Subject: Operating System

Topic: Process Concept and Scheduling

Difficulty: High
operating systems
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1 Answer
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written 4.2 years ago by gravatar for teamques10 teamques10 ★ 70k

First Come First Serve:

Gantt Chart: 

  A    B    C     D      E
0    2    3    11    15    20

Average turnaround time, Waiting time

Job    Arrival Time     Burst Time    Finish Time   Turnaround Time    Waiting time
A       0               2             2             2                  0
B       0               1             3             3                  2
C       0               8             11            11                 3
D       0               4             15            15                 11
E       0               5             20            20                 15
                                      average:      51/5 = 10.2        31/5 = 6.2

Shortest Job First: (Non-Premptive)

Gantt chart:

  B    A    D     E      C
0    1    3    7    12    20

Average turnaround time, Waiting time

Job    Arrival Time     Burst Time    Finish Time   Turnaround Time    Waiting time
A       0               2             3             3                  1
B       0               1             1             1                  0
C       0               8             20            20                 12
D       0               4             7             7                  3
E       0               5             12            12                 7
                                      average:      43/5 = 8.6        23/5 = 4.6

Priority(preemptive):

Gantt chart:

  B    A    A     E    E    C    C    D 
0    1    3    3    8    8    16    16    20

Average turnaround time, Waiting time

Job    Arrival Time     Burst Time    Finish Time   Turnaround Time    Waiting time
A       0               2             3             3                  1
A       0               2             3             3                  1
B       0               1             1             1                  0
C       0               8             16            16                 8
C       0               8             16            16                 8
D       0               4             20            20                 16
E       0               5             8             8                  3    
E       0               5             8             8                  3
                                      average:      75/8 = 9.375        40/8 = 5

Priority(non-preemptive):

Gantt chart:

  B    A     E    C    D 
0    1    3    8    16   20

Average turnaround time, Waiting time

Job    Arrival Time     Burst Time    Finish Time   Turnaround Time    Waiting time
A       0               2             3             3                  1
B       0               1             1             1                  0
C       0               8             16            16                 8
D       0               4             20            20                 16
E       0               5             8             8                  3    
                                      average:      48/5 = 9.6        28/5 = 5.6

Round Robin: (time quantum = 2)

Gantt chart:

  A    B    C     D    E    C    D    E    C    E    C
0    2    3    5    7    9    11   13   15   17   18    20

Average turnaround time, Waiting time

Job    Arrival Time     Burst Time    Finish Time   Turnaround Time    Waiting time
A       0               2             2             2                  0
B       0               1             3             3                  2
C       0               8             20            20                 12
D       0               4             13            13                 9
E       0               5             18            18                 13
                                      average:      56/5 = 11.2        36/5 = 7.2
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