- 2075 Baisakh · 2+2 marks
Page size impact; internal, external fragmentation
Short answer
Small pages reduce internal fragmentation but increase page-table size and faults; large pages improve I/O efficiency but waste more memory. Internal fragmentation is unused space within an allocated block; external fragmentation is free memory split into small non-contiguous holes.
What is the impact of size of page in virtual memory management performance? Define internal and external fragmentation.
Impact of page size on performance
Page size is a trade-off:
| Small pages | Large pages |
|---|---|
| Less internal fragmentation (average waste = half a page per process) | More internal fragmentation |
| Larger page table, more memory for tables | Smaller page table |
| More page faults and more TLB misses/entries needed | Fewer faults, better TLB coverage |
| Many small disk transfers; more seek/rotation overhead per byte | Efficient disk transfer (one seek per large block) |
| Better match to locality; less unused data loaded | May load data that is never used |
According to Tanenbaum, for average process size s and page-table entry size e, the overhead is minimised at page size p = √(2se). Typical sizes are 4 KB to 8 KB.
Internal fragmentation
Wasted memory inside an allocated block or partition because the block is larger than the process needs, so the unused part cannot be given to anybody else. Example: a 9 KB process in 4 KB pages needs 3 pages (12 KB) and wastes 3 KB; a 5 KB process in an 8 KB fixed partition wastes 3 KB. It occurs in paging and fixed partitioning.
External fragmentation
Total free memory is enough for a request, but it is split into small non-contiguous holes, none large enough. Example: holes of 10 K and 15 K cannot satisfy a 20 K request. It occurs in variable partitioning and segmentation; it is cured by compaction (or avoided by paging).
✓ Answer checked by Claude Opus 5.5 (high effort)
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