Difference Between Segmentation and Paging in Operating System (OS)

January 20, 2023

Segmentation And Paging

Memory management in the operating system is an important functionality, which allocates memory to the process for its execution and deallocates the memory when the process is no longer needed There are two management schemes called segmentation and paging in the operating system.

Segmentation

Segmentation is a memory management technique which divides the computer’s primary memory into segments or sections.
It is a scheme in which page is of the variable block size.
In segmentation, the process is divided into two variable size segments, and these segments are loaded into logical memory address space.
The process is segmented module by module. However, in the main memory, the only segment of the process is a store.
The segment table is used to keep the records of the segment, its size, and its memory address.

Priority Scheduling

CPU Scheduling

FCFS Scheduling

Preemptive Scheduling

Paging

Paging is also a memory management scheme.
It allows a process to be stored in the memory in a non-contiguous manner.
It resolves the issue of external fragmentation. In paging, the physical and logical memory spaces are divided into the same fixed-sized blocks.
The blocks of physical memory are called frames, and the blocks of logical memory are called pages.
When a process is executed the process pages from logical memory space are loaded into the frames of physical memory address space.
Then the address generated by CPU for accessing the frame is divided into two parts:- page number and page offset. Page table maps logical address to the physical address.

Paging vs Segmentation

Paging	Segmentation
A page is a physical unit of information.	A segment is a logical unit of information.
Frames on main memory are required	No frames are required
The page is of the fixed block size	The page is of the variable block size
It leads to internal fragmentation	It leads to external fragmentation
The page size is decided by hardware in paging	Segment size is decided by the user in segmentation
It does not allow logical partitioning and protection of application components	It allows logical partitioning and protection of application components
Paging involves a page table that contains the base address of each page	Segmentation involves the segment table that contains the segment number and offset

Learn more about segmentation here.

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