Segmentation

Segmentation is a technique to break memory into logical pieces where each piece represents a group of related information. For example ,data segments or code segment for each process, data segment for operating system and so on. Segmentation can be implemented using or without using paging.

Unlike paging, segment are having varying sizes and thus eliminates internal fragmentation. External fragmentation still exists but to lesser extent.

Address generated by CPU is divided into

• Segment number (s) -- segment number is used as an index into a segment table which contains base address of each segment in physical memory and a limit of segment.
• Segment offset (o) -- segment offset is first checked against limit and then is combined with base address to define the physical memory address.