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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.

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  1. 16 July, 03:36
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    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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