Self doubt

Question

Does fixed size partitioning suffer from external fragmentation?

Answer 1

fixed partition suffers from external and internal fragmentation both if memory is not continous and variable partition suffers from only external fragmentation

Comments

will u explain with an example

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How does “Contiguous Allocation with Fixed-Size Partitions” lead to external fragmentation ??

It doesn’t. 

http://matthews.sites.truman.edu/files/2017/04/chapter8.pdf

https://stackoverflow.com/questions/64454029/can-fixed-partitioning-suffer-from-external-fragmentation

https://stackoverflow.com/questions/39609930/internal-and-external-memory-fragmentation

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No, External Fragmentation is not possible in Fixed Partition. let’s say it like this Even if you got 2 contiguous  free partitions of fixed size 20 & 10 KB in your RAM still you will not be allowed to load a process of 30 KB because its against the rule of fixed partitioning. that’s why external fragmentation is not possible.

( External fragmentation – A form of fragmentation that arises when there is enough memory available to allocate for the process but that available memory is not contiguous.)

Answer 2

Internal fragmentation happens when the space allocated to a requesting process is larger than what is required. This happens in the case of fixed partitioning since the partition sizes are not always same as that requested. 

External fragmentation arises when free memory is separated into small blocks and is interspersed by allocated memory. The result is that, although free storage is available, it is effectively unusable because it is divided into pieces that are too small individually to satisfy the demands of the application. The term "external" refers to the fact that the unusable storage is outside the allocated regions. In case of fixed partitioning, the unusable storage present inside the allocated region cannot be claimed to be external fragmentation. But when there are free partitions formed as a result of freeing up space then there can be external fragmentation. To illustrate this consider three free memory partitions of size 10KB in main memory. A memory request for 10KB  fills up the middle partition. Now a request for 20KB would be declined since, we do not have 20KB that can be allocated contiguously even though the space is available as a whole.

Comments

What if all frames were empty? And 20KB request was made. Would then be it called external fragmentation?

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@Arjun Sir, please verify. For GATE, I guess we can assume that this is indeed external fragmentation.

That's a good doubt. If every process has to fit inside a single partition, it should be considered as external fragmentation since there is unallocated space available, yet cannot be allocated. If a process can span across multiple partitions, it shouldn't be a problem to allocate two 10KB partitions.

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@Arjun sir

Can you please clear this !

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Fixed size partitioning scheme can have both Internal and External fragmentation.

Internal Fragmentation occurs because of fixed size partition, internally space is wasted whenever allocated process has size less than the allotted partition.

External fragmentation actually depends on the size of process request.

• If process request> total available space(either contiguous or non contiguous), then NO External fragmentation, because os cannot assign it.
• If process request<= total available space(and non contiguous), then External fragmentation occurs, because even though we have space available, but still it cannot be allocated. WHY? because memory is NON CONTIGUOUS!

So in above example, when 20KB request comes and 10 KB allotted to middle part, than it leads to external fragmentation of 20KB,

if Process request was 30KB (say >20KB) , then NO external fragmentation would have occurred.

Also Total external fragmentation equals requested process size that couldn't be satisfied, NOT available free space.

say Pi= 16KB ( in above example of 3 fixed partition of 10 kB each), than EF= 16KB ( and NOT 20KB).

Answer 3

NO, it may suffers from INTERNAL FRAGMENTATION bt no EXTERNAL FRAGMENTATION in fixed size partitioning.
Ee : PAGING

Comments

Please explain why there is no external fragmentation. According to what I have read, external fragmentation refers to situation when even though we have total empty memory sufficient for a process but still we couldn't allocate it because memory is not contigous. So according to this definition external fragmentation is possible in fixed partitioning. Please remove my doubt.

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@Digvijay any idea?

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Suffers from Both internal and external fragmentation

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how can it suffer from external fragmentation can anyone explain????

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If two processes of size 20 and 40 are swapped out and a process with size 60 entered then it can not be allocated because it needs 60 units of contiguous memory.Hence external fragmentation.

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if fixed partitioning has two partitions like 20,40  contiguous and space requested  is like 60 then you can't accommodate 60 in this even though it is contiguous, and because it is unspanned we are bound by fixed partitioning so fixed partitioning suffers from internal only not external fragmentation. So fixed have only internal and variable has just external fragmentation fixed doesn't have external fragmentation

Answer 4

yes it will suffer from external fragmentation.