GATE CSE 2017 Set 2 | Question: 08

Question

In a file allocation system, which of the following allocation scheme(s) can be used if no external fragmentation is allowed?

1. Contiguous
2. Linked
3. Indexed

• A. $1$ and $3$ only
• B. $2$ only
• C. $3$ only
• D. $2$ and $3$ only

Comments

External Fragmentaion is only possilbe in Contiguous file Allocation method..

Answer 1

Answer: D) Both Linked and Indexed allocation free from external fragmentation

Refer: Galvin

Reference: https://webservices.ignou.ac.in/virtualcampus/adit/course/cst101/block4/unit4/cst101-bl4-u4-06.htm

Comments

@srestha@Bikram plz let me know if i am wrong

Internal Fragmentation

1) It occurs when memory is divided into fixed-sized partitions.

2) it occurs contiguous & non contiguous allocation

3)non contiguous allocation avoid external fragmentation.

External Fragmentation

1)It occurs when memory is divided into variable-sized partitions based on size of process.

2) it does not occur when memory allocated in non contiguous manner.

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Plz search Wikipedia for it.

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Internal fragmentation happens when the unusable memory is within an allocated memory area.

external fragmentaion happens when the unusable memory is not within an allocated memory area but its still unusable. 

Source

Answer 2

Option D: Both Indexed and Linked file allocation schemes do not suffer from external fragmentation,  Whereas Contiguous allocation suffer from external fragmentation & Internal fragmentation may exist in the last disk block of a file.

Comments

Internal Fragmentation will be there in all the allocations.

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in dynamic memory allocation, memory pools drastically cut internal fragmentation by spreading the space overhead over a larger number of objects.

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@hem chandra joshi @vishalshrm539

IF we have a file of size 1020 B and block size is 512 B

Then every allocation technique will give Internal fragmentation as last block wil  be partially filled 

So all techniques suffer from Internal fragmentation is right ???

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Yes, all will suffer from internal fragmentation given File size is not a multiple of Block size.