Q30,paper 2,D 12.Which of the following memory allocation scheme suffers from external fragmentation ?

(A) Segmentation.

(B) Pure demand paging.

(C) Swapping.

(D) Paging.

Answer(A).

Explanation.

·         Paging suffers internal fragmentation.

·         split physical memory into fixed-sized blocks called frames

·         split logical memory into blocks of same size called pages

·         last page of process may not occupy an entire frame (i.e., some internal fragmentation).

Segmentation suffers from external fragmentation.

• Paging separates the user's view of memory from physical memory.
• segmentation is a memory management scheme which supports the user view of memory
• compiler automatically constructs segments reflecting the input program
• loader assigns these segments segment numbers
• logical address is: (segment name/num, offset)
• segmentation table: an array of (seg base, seg limit) pairs

example (2,53) → (4300+53) = 4353

• eliminates internal fragmentation( because segments are created by compilers like obj is one segment).
• external fragmentation possible.