Segmentation in Memory Management

Segmentation is a memory management scheme that divides a process into different segments, each representing a logical unit of the program, such as the code, data, or stack. Unlike paging, which divides memory into fixed-size blocks, segmentation uses variable-sized segments based on the logical structure of the program.


1. Key Features of Segmentation

Logical Partitioning: Divides memory according to program structure (e.g., code, data, stack).


Variable Segment Sizes: Each segment can have a different size depending on the program's requirements.


Segment Table: The OS maintains a segment table that stores base addresses and limits for each segment.


2. Components of Segmentation

A process is typically divided into these segments:


Code Segment: Contains the program's executable instructions.


Data Segment: Stores global and static variables.


Stack Segment: Holds function calls, local variables, and control information.


Heap Segment: Used for dynamic memory allocation.


3. Address Translation in Segmentation

A logical address in segmentation is made up of:


Segment Number: Identifies the segment.


Offset: The position within that segment.


The operating system uses the segment table to translate the logical address into a physical address.


4. Advantages of Segmentation

Efficient Memory Allocation: Memory is allocated based on the actual needs of the program.


Better Program Organization: Matches the natural structure of the program, such as separating code, data, and stack.


Flexible Memory Sharing: Segments can be shared between different processes.


5. Disadvantages of Segmentation

Fragmentation: External fragmentation can occur as segments vary in size.


Overhead: Requires maintaining a segment table, which adds complexity to memory management.


Complex Address Translation: Each memory access requires looking up the segment table.

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