GATE Overflow Test Series | Operating Systems | Test 2 | Question: 10

Question

Which of the following is/are correct? (Mark all the appropriate choices)

• A. Both the first-fit and best-fit strategies for memory allocation suffer from external fragmentation.
• B. Best-fit strategy for memory allocation avoids internal fragmentation.
• C. Best fit is clearly better than first fit in terms of storage utilization.
• D. Internal fragmentation exists when there is enough total memory space to satisfy a request but the available spaces are not contiguous.

Answer 1

Option A is true.

Best-fit strategy for memory allocation reduces internal fragmentation but may not avoid it completely.

Neither first fit nor best fit is clearly better than the other in terms of storage utilization, but first fit is generally faster.

External fragmentation exists when there is enough total memory space to satisfy a request but the available spaces are not contiguous.

Correct answer: A

Comments

this might be a silly doubt but do help a little.

the best fit and such allocation strategies are used with variable partition scheme where memory is allocated wrt the size of process, first we search for holes of appropriate size and then allocate space and creating smaller holes, these hole accumulate and become large enough to fit a process together but not alone and causing external fragmentation.

as for fixed allocation scheme the block are all of same size hence when memory is allocated entire chunk belongs to the process yet some of it is not used since size of process is smaller than or equal to size of block, thus causing internal fragmentation.

so in such cases do we need to use best fit or first fit allocation strategies to search for block when all are of same size.

which book should i study this topic from for more detail?

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@Deepak Poonia

in option B, 

Best-fit strategy for memory allocation reduces internal fragmentation but may not avoid it completely.

it is not asking for avoid completely, that is elimination i think. 

Best fit searches the entire list, from beginning to end, and takes the smallest hole that is adequate

doing this, it is avoiding IF.