Difference Between Paging And Segmentation

Difference Between Paging And Segmentation

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Rashmi
Rashmi Karan
Manager - Content
Updated on Sep 11, 2023 17:57 IST

The main difference between Paging and Segmentation is that Paging divides memory into fixed-size blocks called pages, while Segmentation divides memory based on data type or function into variable-sized segments.

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Memory management is key in optimizing computer memory utilization by minimizing internal and external fragmentation. As systems handle various processes, memory allocation can occur in either contiguous (adjacent) or non-contiguous (non-adjacent) ways, depending on the availability of memory partitions. Paging and segmentation are two important non-contiguous memory allocation techniques to manage memory efficiently. In is blog, we will cover the key differences between paging and segmentation.

What is Paging?

Paging is a memory management technique used in operating systems to manage the memory of a computer system efficiently. Paging allows storing a process in memory in a non-contiguous manner. The storage process in a non-contiguous manner solves the problem of external fragmentation.

Fig 1 – Paging divides the memory into fixed-size blocks called pages, and the Memory Management Unit (MMU) translates virtual addresses used by the CPU into physical addresses in the memory, allowing seamless and optimized data access.

Understand paging with an analogy –

Analogy: Imagine you have a photo album with pages that are the exact size of your photos. However, your photos come in different sizes and might not always fit perfectly onto a single album page. This is similar to how programs and data load into a computer’s memory and divided into fixed-size units called frames.

Technical Insight: In a computer’s memory management, the photo album analogy relates to the virtual memory system, while the individual photos represent chunks of a program or data.

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Features of Paging

  1. Paging allows non-contiguous (not adjoining) allocation of physical memory, thereby eliminating external fragmentation and making more efficient use of memory space.
  2. Paging uses a uniform page size, simplifying memory management for the operating system.
  3. Each page can have its permissions, allowing the operating system to control access to different memory regions. It detects and prevents any unauthorized access.
  4. Paging’s address translation process is simpler and faster, involving just a few memory accesses, ensuring good system performance.
  5. Paging forms the basis for virtual memory systems, allowing the computer to run programs larger than the physical memory by swapping pages in and out of disk storage.
  6. Paging combines with other memory management techniques, such as Segmentation, to balance flexibility and simplicity.

What is Segmentation?

Segmentation is a memory management technique used in computer systems where the structure of a program reflects its logical division. This involves dividing a program into segments, blocks of variable size that contain related information. Each segment typically corresponds to a logical program unit, such as a subroutine, data structure, or arrangement.

Fig 2 – Segmentation enhances a computer’s information retrieval efficiency by grouping related data into segments, each represented in a table. This table bridges the CPU and the physical memory, enabling faster access to specific data types or functions. This logical separation promotes optimized memory management and controlled data access within the system.

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Understand segmentation with an analogy –

Analogy: Imagine your computer’s memory as a large bookshelf with dividers. Each section represents a segment where you place books (data) related to specific topics. This keeps related information organized and together.

Technical Insight about Segmentation: Memory segmentation divides the computer’s memory into segments designated for a specific purpose or data type.

This analogy illustrates how memory segmentation organizes and manages data within a computer’s memory, promoting efficiency, isolation, and effective memory utilization.

Features of Segmentation

  • Each program segment (logical unit) is treated as a separate module for easy maintenance and development.
  • Segmentation accommodates variable-sized data structures like stacks. This flexibility is particularly useful for data structures that dynamically change size during program execution.
  • Segments can be protected against unauthorized access through access restrictions. 
  • The security of segments can be enhanced by preventing unintended or unauthorized interactions with sensitive data.
  • Segments can be shared among multiple processes.
  • Segmentation allows links between segments to be established only when needed. This can help reduce startup time and memory consumption.
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Difference Between Paging And Segmentation

Paging Segmentation
Unit of Division Fixed-size blocks (pages) of both virtual and physical memory. Variable-sized logical segments of a program.
Memory Mapping Uses page tables to map virtual addresses to physical addresses. Uses segment tables to map logical addresses to physical addresses.
Address Translation Virtual address split into page number and offset. Page table lookup is needed. Logical address directly translated using segment number and offset. Segment table lookup is needed.
Sizes Uniform size for both pages and frames. Variable sizes for segments.
Fragmentation Eliminates external fragmentation but may have internal fragmentation. May lead to external fragmentation due to varying segment sizes.
Memory Protection Page-level permissions apply for each page. Segment-level permissions can be set for different segments.
Efficiency Address translation is efficient due to fixed-size pages. Address translation can be less efficient due to variable segment sizes.
Flexibility Limited flexibility in accommodating program structure. Flexible as it maps to the program’s logical structure.
Usage Used in combination with other techniques like segmentation (paged segmentation). Primarily used when programs have distinct parts like code, data, and stack.
Complexity Relatively simpler memory management mechanism. More complex management due to variable segment sizes.
Virtual Memory Forms the basis for virtual memory systems. Can be used in virtual memory systems along with paging.
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Key Takeaways

  • Paging simplifies memory management and reduces external fragmentation.
  • Segmentation supports the logical separation of different data types or tasks.
  • Paging doesn’t provide logical separation of data types or functions.
  • Segmentation requires more complex address translation involving segment tables and offers better protection and access control due to isolated segments.

Both paging and segmentation aim to optimize memory utilization, but they employ different approaches. The choice between them depends on the specific requirements and constraints of the computing environment.

FAQs

How does Paging divide memory compared to Segmentation?

Paging divides memory into fixed-size blocks called pages, while Segmentation divides memory based on data type or function into variable-sized segments.

How are memory units treated in Paging and Segmentation?

In Paging, memory units are uniform and treated as equal pages. In Segmentation, memory units are segments that can vary in size and hold specific types of data.

Which technique is more prone to external fragmentation and why?

Segmentation is more susceptible to external fragmentation due to the varying sizes of segments that can lead to unused memory gaps.

How does Paging handle internal fragmentation?

Paging eliminates internal fragmentation by dividing memory into fixed-size pages, ensuring each page is fully utilized.

Can Paging inherently offer logical separation of data like Segmentation does?

No, Paging does not inherently provide logical separation of data; data can be scattered across pages. Segmentation allows for the logical grouping of related data within segments.

What factors influence the choice between Paging and Segmentation in memory management?

The choice depends on factors such as the nature of applications, memory requirements, trade-offs between isolation and efficiency, and the specific constraints of the computing environment.

About the Author
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Rashmi Karan
Manager - Content

Rashmi is a postgraduate in Biotechnology with a flair for research-oriented work and has an experience of over 13 years in content creation and social media handling. She has a diversified writing portfolio and aim... Read Full Bio