What is segmentation and how does it differ from paging?

Segmentation divides memory into variable-sized segments based on logical units (code, data, stack). Each segment has base address and limit. Provides programmer-visible memory organization and protection per segment. Vs Paging: Paging uses fixed-size pages (invisible to programmer), segmentation uses variable-size segments (programmer visible). Segmentation can have external fragmentation; paging has internal. Some systems combine both (segmented paging) - each segment is paged.