Paged Segmentation and Segmented Paging
Segmentation with paging is a memory management technique used in operating systems to overcome the limitations of pure segmentation or pure paging. It combines the benefits of both approaches to provide efficient and flexible memory management. Let’s explore how segmentation with paging works and its advantages.
Segmented Paging
Segmentation divides the logical address space of a process into segments, where each segment represents a different type of data or code. Segments can vary in size and are assigned unique identifiers. Each segment has a base address and a limit that define its location and size within the logical address space.
Segmentation provides the following advantages:
- Allows logical division of a program into modules or data structures
- Supports sharing of code and data between processes
- Simplifies memory protection and access control
However, pure segmentation suffers from external fragmentation, as segments can be of different sizes and may leave unused gaps of memory between them.
What is Paging ?
Paging divides the physical memory into fixed-size blocks called pages. The logical address space of a process is also divided into fixed-size blocks called pages. Each page is assigned a unique identifier called a page number.
Advantages of using Paging:
- Simplifies memory management by using a fixed-size unit of allocation
- Reduces external fragmentation as all memory blocks are of the same size
- Supports efficient memory allocation and deallocation
Disadvantages of using Paging:
- This scheme may suffer ‘page breaks’.
- If the number of pages is high, it is difficult to maintain page tables.
Segmentation with Paging:
Segmentation with paging combines the benefits of segmentation and paging to provide a more efficient and flexible memory management scheme.
In this technique, the logical address space is divided into segments, similar to pure segmentation. However, each segment is further divided into fixed-size pages, as in pure paging. This creates a two-level hierarchical structure, where segments are the top-level units and pages are the second-level units.
Advantages of Segmentation with Paging:
The advantages of segmentation with paging include:
- Efficient memory allocation and utilization due to fixed-size pages
- Logical division and modular structure provided by segments
- Reduced external fragmentation as pages are of the same size
- Flexibility in managing code and data within a process
To translate a logical address in segmentation with paging, both the segment number and the page number are used to determine the physical address. The segment table is consulted first to obtain the base address of the segment, and then the page table is consulted to obtain the physical address within the segment.
By combining the advantages of segmentation and paging, this technique offers a flexible and efficient memory management solution for operating systems.
