Nov2017 cs Q49

0. Consider the following four processes with the arrival time and length of CPU burst given in milliseconds :
Process Arrival Time Burst Time
P₁ 0 8
P₂ 1 4
P₃ 2 9
P₄ 3 5
The average waiting time for preemptive SJF scheduling algorithm is __________.

Answer
Comment
Array

Option : A
Explanation :
First we will make gantt chart of given process then we will calculate turn around time and waiting time of individual process.

Now we have to calculate average waiting time for schedule:
avg waiting time = wt(P1 + P2 + P3 + P4 )/number of process.
ie. (9 + 0 + 15 + 2) / 4
= 26 / 4
= 6.5
So, option (A) is correct.

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