Difference Between Paging and Segmentation

By : Nathaniel Brooks Nathaniel Brooks
Hours Updated

Key Difference between Paging and Segmentation in OS

  • A page is of fixed block size, whereas a segment is of variable size.
  • In Paging, the hardware decides the page size, while the segment size is specified by the user.
  • The paging technique is faster for memory access, but segmentation is slower than the paging method.
  • In Paging, the user just provides a single integer as the address, while in segmentation, there is the availability of many independent address spaces.
  • Page table stores the page data, while the segmentation table stores the segmentation data.

Difference Between Paging and Segmentation
Difference Between Paging and Segmentation

Here, I have analyzed the difference between Paging and segmentation and will comprehensively evaluate their pros and cons.

What is Paging?

Paging is a storage mechanism that allows the OS to retrieve processes from secondary storage into the main memory in the form of pages. In the Paging method, the main memory is divided into small fixed-size blocks of physical address, which are called frames. The size of a frame should be kept the same as that of a page to have maximum utilization of the main memory and to avoid external fragmentation. Paging is used for faster access to data, and it is a logical concept.

What is Segmentation?

Segmentation method works almost similarly to Paging, the only difference between the two is that segments are of variable length, whereas in the paging method, pages are always of fixed size. A program segment includes the program’s main function, data structures, utility functions, etc. The OS maintains a segment map table for all the processes. It also includes a list of free memory blocks along with their size, segment numbers, and memory locations in the main memory, or virtual memory.

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Difference between Paging and Segmentation

In my experience with OS, I’ve observed the following differences between Paging and Segmentation:

Paging vs Segmentation
Paging vs Segmentation
Sr. No. Paging Segmentation
1. A page is of the fixed block size. A segment is of variable size.
2. It may lead to internal fragmentation. It may lead to external fragmentation.
3. In Paging, the hardware decides the page size. The segment size is specified by the user.
4. A process address space is broken into fixed-sized blocks, which are called pages. A process address space Is broken into differing-sized blocks called sections.
5. The paging technique is faster for memory access. Segmentation is slower than the paging method.
6. Page table stores the page data Segmentation table stores the segmentation data.
7. Paging does not facilitate any sharing of procedures. Segmentation allows for the sharing of procedures.
8. Paging fails to distinguish and secure procedures and data separately. Segmentation can be used to separate secure procedures and data.
9. Paging address space is one-dimensional In segmentation, there is the availability of many independent address spaces
10. In Paging, the user just provides a single integer as the address, which is divided by the hardware into a page number and offset. In the segmentation method, the user specifies the address in two quantities
1) segment number 2) offset.

Advantages of Paging

Now, let me share the advantages of using the paging method:

  • Easy to use memory management algorithm
  • No need for external Fragmentation
  • Swapping is easy between equal-sized pages and page frames.

Disadvantages of Paging

Here, I outline the cons of Paging:

  • May cause internal fragmentation
  • Page tables consume additional memory.
  • Multi-level Paging may lead to memory reference overhead.

Advantages of Segmentation

From my experience, the benefits of segmentation are clear.

  • Offer protection within the segments
  • You can achieve sharing by segmenting and referencing multiple processes.
  • Not offers internal fragmentation
  • Segment tables use less memory than Paging

Disadvantages of Segmentation

Here are the drawbacks of segmentation i have identified.

  • In the segmentation method, processes are loaded or removed from the main memory. Therefore, the free memory space is separated into small pieces, which may create a problem of external fragmentation
  • Costly memory management algorithm

How to Choose Between Paging and Segmentation

I have personally found that while paging simplifies memory management, segmentation provides tailored solutions that enhance process management. We should choose based on the specific needs of the application environment.