The document discusses segmentation as a memory-management scheme that allows programmers to view memory as a collection of logical units, such as functions and variables. It explains the structure of a logical address as a tuple consisting of a segment number and offset, and details the role of segment tables in mapping addresses and managing memory limits. Additionally, it includes references to external resources for further reading on the topic.

1. Welcome!!
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2. CS206 Operating System
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3. Tip of The Day
discourager.ignore();
(Courtesy: Syed Hammad Ahmed – CS@DSU)
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4. Recap:
• Contiguous Memory
• Fragmentation
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5. Segmentation
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6. Segmentation:
Memory-management scheme that supports user view of memory
(Programmar’s View).
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
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7. User’s View of a Program:
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8. Logical View of Segmentation
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user space physical memory space
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9. Segmentation :
Each segment has a name and length
Address specify both the segment name and offset
Instead of using name the segments are numbered
The logical address consists of a tuple:
<segment-number,offset>
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10. Segmentation Architecture:
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;
segment number s is legal if s < STLR
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11. Segmentation Hardware:
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12. Segmentation Hardware:
Logical address generated by CPU consists of two parts
Segment no. ‘s’:-used as a index into segment table
Offset ‘d’:- must be between ‘0’ and segment limit
A trap is generated if offset exceeds the segment limit
(Correct offset + segment base = address in physical memory)
Segment table is an array of base-limit register pair
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13. Siraj Munir – CS@DSU
Questions??
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14. Siraj Munir – CS@DSU
Reference:
https://www.youtube.com/watch?v=HWwNTWY1rxo
http://www.slideshare.net/rajmohan50/paging-and-segmentation-in-operating-system
https://classroom.udacity.com/courses/ud923/lessons/301489
8657/concepts/30515485910923#
https://en.wikibooks.org/wiki/Operating_System_Design/Segmentation
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15. Siraj Munir – CS@DSU
Thankyou!
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