UGC NET CSE | June 2014 | Part 2 | Question: 34

Question

Match the following $:$

$\begin{array}{clcl}   \text{} & \textbf{List – I} && \textbf{List – II} \\ \text{a.} & \text{Contiguous allocation} & \text{i.} & \text{This scheme supports very large}\\&&& \text{ file sizes.} \\ \text{b.} & \text{Linked allocation} & \text{ii.} & \text{This allocation technique supports}  \\ &&& \text{ only sequential files.}  \\  \text{c.} & \text{Indexed allocation} & \text{iii.} & \text{The number of disks required to} \\&&&\text{access file is minimal.} \\ \text{d.} & \text{Multi-level indexed} & \text{iv.} & \text{This technique suffers from maximum} \\ &&&\text{wastage of space in storing pointers.}  \\   \end{array}$

$\textbf{Codes :}$

• A. $\text{a-iii; b-iv; c-ii; d-i}$
• B. $\text{a-iii; b-ii; c-iv; d-i}$
• C. $\text{a-i; b-ii; c-iv; d-iii}$
• D. $\text{a-i; b-iv; c-ii; d-iii}$

Answer 1

Answer is B).

Contiguous allocation ---> Number of disks required to access file is minimal.

Linked allocation ---> This allocation technique supports only sequential files

Indexed allocation --->  This technique suffers from maximum wastage of space 

Multi-level indexed  ---> This scheme supports very large file sizes

Answer 2

Contiguous Allocation

• Files are stored in a contiguous manner, ie, the file is stored in sequential, next-door blocks.
• Because of this, the R/W head movement is minimal (minimal seek time).
• Suffers from external fragmentation.

Linked Allocation

• It is essentially a linked-list of blocks, which we use to store the file.
• The user has access to only the pointers of the first and the last node, not the intermediate nodes. For this reason:-

1. Not suitable for random access.
2. If a block size is 512 B, and pointer size is 4 B, user sees the block as of 508 B.

• Lots of space is wasted on storing pointers.
• Unreliable (what if we lose an intermediate pointer?)

Indexed Allocation

• Same as Linked Allocation, but all the pointers are brought together in a file called the index file.
• Hence, the user has access to all the pointers, and may perform random access.
• Maximal wastage of storage is observed in Indexed Allocation as other than the pointers, it also creates additional file for the indices.

Option B

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Related: Internal vs External Fragmentation.

Comments

you are contradicting the answer you have given ,
you are listing lots of space is wasted on storing pointers as one of the disadvantages of linked allocation ..
So option must be a.

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Read the last point of Indexed Allocation carefully.

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That's why i got confused..I will stick with Kapil ji