Which statement best describes the differences between paging and segmentation?

• A. Paging uses fixed-size pages for simple mapping and no external fragmentation; segmentation uses variable-sized segments for logical grouping but can suffer fragmentation; most systems combine them using paged segmentation.
• B. Segmentation uses fixed-size pages for mapping and avoids fragmentation.
• C. Paging uses variable-sized pages for mapping and always avoids fragmentation.
• D. Paging and segmentation are identical in memory management.

Answer: (A)

Paging and segmentation approach memory in fundamentally different ways. Paging breaks the virtual address space into fixed-size pages that map to fixed-size physical frames. This uniformity makes the mapping straightforward via a page table and largely eliminates external fragmentation because free memory is managed in equal blocks that can be scattered anywhere in physical memory. A trade-off, though, is internal fragmentation: the last page of a process may not be fully used, leaving some wasted space inside that page.

Segmentation, on the other hand, divides memory into variable-sized segments that correspond to logical units like code, data, or stack. Because segments must fit contiguously in physical memory, allocation can suffer external fragmentation, where enough total memory exists but not in a large enough contiguous block to hold a segment. This model aligns with meaningful program structure, but its fragmentation behavior differs from paging.

Many systems blend the two ideas with paged segmentation or segmented paging, using segments for logical organization while paging within each segment to map to fixed-size frames. This combines the organizational clarity of segmentation with the fragmentation advantages of paging.