In a batch operating system, three jobs are submitted for execution. Each job involves an I/O activity, CPU time and another I/O activity of the same time span as the first. Job JOB1 requires a total of 23 ms, with 3 ms CPU time; JOB2 requires a total time of 29 ms with 5 ms CPU time; JOB3 requires a total time of 14 ms with 4 ms CPU time. Illustrate their execution and find CPU utilization for uniprogramming and multiprogramming systems.

a) CPU utilization for uniprogramming system = 18.2%

b) CPU utilization for multiprogramming system = 41.379%

Explanation:

IO time = total time – CPU time

For JOB 1  

CPU time = 3ms ,

total time= 23ms

IO time = 23-3 = 20ms ,

For JOB 2

CPU time =5ms

total = 29ms

IO time = 29-5 = 24ms  

For JOB 3  

CPU time = 4ms

total = 14ms

IO time = 14-10 =10ms  

1.) In uniprogramming system, operations are performed sequentially

CPU utilization=total CPU time / total real time

CPU utilization =(3+5+4) / (23+29+14)

CPU utilization =0.182 or 18.2%

2) In multiprogramming system, jobs wait for the CPU to get free while performing IO operations concurrently

steps followed by the os

1.IO for 1st job                           at 0ms

2.IO for 2nd job                          at 0ms

3.IO for 3rd job                          at 0ms

4.CPU time for 3rd job              at 5ms

5.Next IO job for 3rd job           at 9ms END at 14ms

6.CPU time for 1st job              at 9ms

7.Next IO job for 1st job           at 14ms END at 23ms

8.CPU time for 2nd job             at 14ms

9.Next IO job for 2nd job          at 15ms END at 29ms

CPU time is 3+5+4 =12ms

Total execution time = 29ms

CPU utilization = 12*100/29= 41.379%

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