2.2k views

A computer installation has 1000k of main memory. The jobs arrive and finish in the following sequences.

    Job 1 requiring 200k arrives
Job 2 requiring 350k arrives
Job 3 requiring 300k arrives
Job 1 finishes
Job 4 requiring 120k arrives
Job 5 requiring 150k arrives
Job 6 requiring 80k arrives
1. Draw the memory allocation table using Best Fit and First Fit algorithms

2. Which algorithm performs better for this sequence?

edited | 2.2k views

Initial there is $1000k$ main memory available.

Then job $1$ arrive and occupied $200k$, then job $2$ arrive, occupy $350k$, after that job $3$ arrive and occupy $300k$ (assume continuous allocation ) now free memory is $1000-850(200+350+300)= 150k$ (till these jobs first fit and best fit are same)

Now, job $1$ is finished. So, that space is also free. So, here $200k$ slot and $150k$ slots are free.

Now, job $4$ arrives which is $120k$.

Case 1:

• First fit, so it will be in $200$ k slot (free slot ) and now free is $= 200-120=80k$,
• Now $150k$ arrive which will be in $150$ $k$ slot
• Then, $80k$ arrive which will occupy in $80k$ slot $(200-120)$ so, all jobs will be allocated  successfully.

Case 2:

• Best fit : $120 k$ job will occupy best fit free space which is $150k$ so, now remaining $150-120=30k$,
• Then $150k$ job arrive it will be occupied in $200k$ slot, which is best fit for this job. So, free space $=200-150= 50$,
• Now, job $80k$ arrive, but there is no continuous $80k$ memory free. So, it will not be allocated successfully.

So, first fit is better.

by Boss (17.1k points)
edited
+2
There is external fragmentation problem if we use Best fit here. Because of which 80k request is denied ...
0
nice eplanation @ sonam vyas
First fit, in best fit 80K will not be served
by Junior (883 points)

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