Question

Consider the following set of processes, with the length of the CPU-burst time given in milliseconds:

Process            Burst Time Priority

P1                               5 4

P2                               3 1

P3                               1 2

P4                               7 2

P5                               4 3

The processes are assumed to have arrived in the order P1, P2, P3, P4, P5, all at time 0.

If nonpreemptive priority (a larger priority number implies a higher priority) is used, what is the average waiting time of these processes?

Answer 1

In the Non Preemptive Priority scheduling, Processes are scheduled according to their priority. higher priority process exexute first.

Given that larger priority number implies a higher priority, so higher priority process exexute first.

GANTT Chart :

P4

P1

P5

P2

P3

0 72 126 169   200   212

Turnaround Time=Completion Time - Arrival Time  

Waiting Time=Turn Around Time - Burst Time

Process Id	Arival Time	Burst Time	Completion Time	Turnaround Time	Waiting Time
P4	0	72	72	72	0
P1	0	54	126	126	72
P5	0	43	169	169	126
P2	0	31	200	200	169
P3	0	12	212	212	200

average waiting time=sum(Waiting Time)/(Number of process)

Sum(Waiting Time)=0+72+126+169+200

=567

Number of process=5

average waiting time=567/5

average waiting time=113.4