Question

scheduling algorithm with reason.

You have five (5) memory partitions of 180 MB, 590 MB, 280 MB, 380 MB, 700 MB which is in order, Do the best-fit, first-fit and worst-fit algorithms place processes of 315 MB, 420 MB, 230 MB, and 530 MB? Find the algorithm which makes the best use of the memory?

Answer 1

Solution:

We have five (5) memory partitions of 180 MB, 590 MB, 280 MB, 380 MB, 700 MB and processes of 315 MB, 420 MB, 230 MB, and 530 MB.

a) First-fit

The first-fit algorithm selects the first free partition that is large enough to accommodate the request.

First-fit would allocate in the following manner:

• 315 MB => 590 MB partition, leaves a 275 MB partition
• 420 MB => 700 MB partition, leaves a 280 MB partition
• 230 MB => 280 MB partition, leaves a 50 MB partition
• 530 MB would not be able to allocate, no partition large enough!

b) Best-fit

The best-fit algorithm selects the partition whose size is closest in size (and large enough) to the requested size.

Best-fit would allocate in the following manner:

• 315 MB => 380 MB, leaving a 65 MB partition
• 420 MB => 590 MB, leaving a 170 MB partition
• 230 MB => 280 MB, leaving a 50 MB partition
• 530 MB => 700 MB, leaving a 170 MB partition

c) Worst-fit

The worst-fit algorithm effectively selects the largest partition for each request.

Worst-fit would allocate in the following manner:

• 315 MB => 700 MB, leaving a 385 MB partition
• 420 MB => 590 MB, leaving a 170 MB partition
• 230 MB => 380 KB, leaving a 150 MB partition
• 530 MB would not be allowed to allocate as no partition is large enough!

d) Which algorithm makes the most efficient use of memory?

The best-fit algorithm performed the best of the three algorithms, as it was the only algorithm to meet all the memory requests.

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