Segmented Paging: Combining Segmentation and Paging for Efficient Memory Management

Explore segmented paging, a hybrid memory management technique combining segmentation and paging. This guide explains how segmented paging works, its advantages over pure segmentation and paging, and how it addresses memory management challenges in operating systems.

Segmented Paging

What is Segmented Paging?

Segmented paging combines the benefits of both segmentation and paging memory management techniques. Pure segmentation isn't widely used due to certain limitations, but combining it with paging addresses these issues. In segmented paging, memory is divided into variable-sized segments, which are further subdivided into fixed-sized pages.

Think of it like this: you have large file cabinets (segments) and each file cabinet is divided into smaller drawers (pages) of a uniform size. The pages are smaller than the segments.

Address Structure and Translation

Each segment has its own page table. A logical address is broken down into three parts:

  • Segment Number: Identifies the specific segment.
  • Page Number: Identifies the page within the selected segment.
  • Page Offset: Specifies the location within the page.

The segment table contains an entry for each segment, pointing to its corresponding page table. The page table then maps the page number to its physical frame number in main memory.

To translate a logical address to a physical address, the CPU first uses the segment number to find the correct segment table entry. Then, the page number is used to locate the frame number within the segment's page table. Finally, the page offset is added to the frame number to get the final physical address.

Advantages of Segmented Paging

  • Reduced memory usage: Page tables are smaller because they are per segment.
  • Limited page table size: The size of a page table is proportional to the segment size.
  • Simplified segment table: Only one entry per segment is needed in the segment table.
  • No external fragmentation: Segments can be of variable sizes, eliminating external fragmentation.
  • Simplified memory allocation: Allocation becomes more efficient.

Disadvantages of Segmented Paging

  • Internal fragmentation: Pages are fixed size, so there might be wasted space within a page.
  • Increased complexity: More complex to implement than pure paging.
  • Contiguous page tables: Page tables must be stored contiguously in memory.

C Code Example: Declaring a Character Variable

Syntax

char ch = 'a';

Example Output

Output

She said "Hello!" to me.

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