Segmentation topic is presented in a most easy way. Segmentation is a user view of memory in Operating System. Segmentation is one of the most common ways to achieve memory protection. In a computer system using segmentation, an instruction operand that refers to a memory location includes a value that identifies a segment and an offset within that segment.

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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