The document discusses Unix and Linux virtual memory, specifically focusing on memory management through segmentation. It explains how a program consists of segments, each with a logical address composed of a segment number and offset, and outlines the advantages and disadvantages of segmentation compared to paging. The document also covers the structure of segment tables and the impact of segmentation on memory usage.

1. TOPIC:-UNIX VIRTUAL MEMORY,
LINUXVIRTUAL MEMORY &
VIRTUAL MEMORY USING SEGMENTATION
NAME:- TARUN TIWARI
ROLL NO.:- MCA/25007/18
CLASS:- MCA 2nd SEM.

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UNIX VIRTUAL MEMORY

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LINUX VIRTUAL MEMORY

4.  Memory – Management scheme that supports user view of memory
 A program is a collection of segments
• A segment is a logical unit such as:
 Main program
 Procedure
 Function
 Method
 Object
 Local variables, global variables
 Common block
 Stack
 Symbol table
 Arrays

5.  Logical address consists of a two tuple:
<segment-number, offset>,
 SEGMENT TABLE – maps two – dimensional physical addresses;
each table entry has:
-- BASE – contains the starting physical address where
the segments reside in memory
--LIMIT – specifies the length of the segment
 SEGMENT- TABLE BASE REGISTER (STBR) points to the segment
table’s location in memory
 SEGMENT- TABLE LENGTH REGISTER (STLR) indicates number of
segments used by a program;

6. Advantages of Segmentation –
 No Internal fragmentation.
 Segment Table consumes less space in comparison to Page table in paging.
Disadvantage of Segmentation –
 As processes are loaded and removed from the memory, the free memory space is broken
into little pieces, causing External fragmentation.

7. VIRTUAL ADDRESS SEGMENTATION
 Each process is divided into a number of segments, not all of
which are resident at any one point in time.

8. Example: Effective Address Calculation in Segmentation
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9. THANK YOU