How does the Next Fit algorithm work in below screenshot ?

Question

Comments

I am not getting how 50 bytes request is satisfied by 170 bytes block and not free area after  100 bytes ?

Answer 1

Next fit is a modified version of First Fit. It begins as first fit to find a free partition but when called next time it starts searching from where it left off, not from the beginning. 

Reference:Next Fit

Answer 2

In this question we have 3 free memory spaces of size:200 , 170 and 500. We have to allocate memory to 3 processes of size 100, 50 and 400 bytes. The next fit algorithm selects the next free location if possible for the process.Next fit  begins as first fit to find a free partition but when called next time it starts searching from where it left off i.e . after 100 was allocated, not from the beginning.So for the first time when we have to allocate memory to the block of size 100 the block of free memory of size 200 is encountered and we use it. Then we dont see how much memory is left with it we move to the next partition of size 170 and out of that the required memory is allocated to it. Similarly for 400 , the 500 size free partition is chosen in this example.

Comments

Can you please explain if request for 50 bytes is chosen from partition of size 170 , then why is the list of free pointer is starting just after it allocated 100 bytes inside 200 bytes block ?

That means we have variable partitioning here .

So we should start allocating next request as soon as we find a free space area .

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ya it means that we are having variable size partitioning in this case and that is why it is pointing to 100.

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So here the free area  pointer is just pointing to the next free area after 100 bytes , so we should place 50 bytes just after the free area of 100 bytes na , why to go to 170 bytes partition ?

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In the case of first fit we did that only.. but in next fit as satted in the ans we will go to the next position i.e when searching for a slot for the 50 bytes first we encounter 100 bytes slot then next we encounter 170 bytes and so we choose it(as it is next fit).This is the reason we go to the 170 bytes partition.