[cs33211] Project 2 computing average wait time and turnaround time

[Porter, David]

Dr. Foreback,

I think there might be an error in the second formula:
P3 turn around time = (24-3) = 31

Should be:
P3 turn around time = (24-3) = 21

I kept trying to get my code for average turnaround time to equal 22.67 and then recalculated everything.

David


From: cs33211-bounces at cs.kent.edu [mailto:cs33211-bounces at cs.kent.edu] On Behalf Of Dianne Foreback
Sent: Friday, March 17, 2017 4:51 PM
To: cs33211 at cs.kent.edu
Subject: [cs33211] Project 2 computing average wait time and turnaround time

Hello OS Class:

Project 1 output has a slight mistake for the FCFS average turnaround time.  It should be 22.67.

I've had a couple questions on how to compute the average wait time and average turnaround time.  My explanation relates to the FCFS scheduling algorithm using the input from project 1.

pid       arrival  burst
---------------------
1          0          10
2          0          9
3          3          5
4          7          4
5          10        6
6          10        7

The average wait time is the average amount of time each process waits in the readyQ.
So, for each process the wait time is the time the process gets access to the CPU minus
the time the process arrives.
P1 wait time is (0 - 0) = 0
P2 wait time is (10 - 0) = 10
P3 wait time is (19-3) = 16
P4 wait time is (24-7) = 17
P5 wait time is (28-10) = 18
P6 wait time is (34-10) = 24
To get the average, add all of these together and divide by 6:
(0+10+16+14+18+24)/6 = 14.17

The average turnaround time is the average amount of time that it takes from the time it is
submitted to the time it finishes.  So, for our project, this is the average amount of time starting from when the process finishes minus the time the process arrives.
P1 turn around time = (10-0) = 10
P2 turn around time = (19-0) = 19
P3 turn around time = (24-3) = 31
P4 turn around time = (28-7) = 21
P5 turn around time = (34-10) = 24
P6 turn around time = (41-10) = 31
To get the average, add all of these together and divide by 6:
(10 + 19+31+21+24+31)/6 = 22.67

Best,
Dianne
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