Made Easy: Memory allocation

Question

Consider 900 KB memory is managed using variable partitions but no compaction. It currently has three process occupied partition of sizes 212 KB, 114 KB and 100 KB respectively. What is the smallest allocation request that could be denied?

Comments

@OneZero

we don't know how the requests are allocated previously. they can be allocated all together or all farther apart. since we know nothing about that, we have to consider the worst way they are allocated.

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But then they said which of the following request would be denied. According to me the answer should be none of these only when we can fit in a block that is greater than the max given options.

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since we don't know how previous allocation of process is done which can vary from 474 (all together -best case) to 118 ( apart from each other -worst case), we need to go for 120KB! @aambazinga you are correct! 

Answer 1

Complexity lies in this question is.... how much size of small holes can you created?

 

with n processes ==> you can create minimum 1 hole ===> you can identify The maximum Process can be denied

P1	P2	P3	hole
212	114	100	474

Therefore if a process comes with size 475 KB you can't allocate.

 

with n processes ==> you can create maximum n+1 holes ===> you can identify The minimum Process can be denied

hole	P1	hole	P2	hole	P3	hole
	212		114		100

 

     hole size = $\frac{Total \; size\; available}{no.of holes}$ = $\frac{474}{4}$ = 118.5

 Therefore two holes get 118 KB and two holes can get 119 KB

Therefore if a process comes with size 120 KB you can't allocate.

 

( if you have doubt that why holes must be equal size, then if you decrease size of one hole then one of the remaining holes size must be increased then you can allocate 120 KB process )

Comments

@Shaik Masthan 

 it is written like this in the real question in addition to the asked question " which of the following memory allocation request that could be denied?:

A) 475

B) 285

C) 355

D) None of the above 

 

Answer given is A here but the smallest request that can be denied is 119 but nowhere it is written in the option hence according to the options we should select option B as it is the smallest request given in the options that could be denied ryt??

Correct me.

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yes, you can choose B,

it is actually similar to a GATE question, testseries admin want to modify it !

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Exactly it means I deserve a few more marks on my test series!! What a blunder.