38 paged segmentation
- 1. Storage Management • Paged Segmentation 1
- 2. HOME PREVIOUS TOPIC NEXT PREVIOUS QUESTION PAPERS FOR OS CPP TUTORIALS 2
- 3. Recap… In the last class, you have learnt: Paging concepts and segmentation Pages Frames Segments 3
- 4. Objective On completion of this period, you would be able to know • Paged Segmentation 4
- 5. Segmentation with Paging – MULTICS • The MULTICS system solved problems of external fragmentation and lengthy search times by paging the segments • Paging eliminates external fragmentation • Segment-table entry contains the base address of a page table for that segment 5
- 6. Segmentation with Paging – MULTICS • In MULTICS logical address = 18-bit segment no. + 16-bit offset • This scheme creates a 34-bit address space • Each page in MULTICS consists of 1 K words • So the segment offset is broken in to 6-bit page no. and 10-bit page offset • Page no. indexes into the page table to give the frame no. • Frame no. is combined with the page offset to form a physical address 6
- 7. Segmentation with Paging – MULTICS • Must have a separate page table for each segment • The 18-bit segment no. could have up to 2,62,144 segments • So the 18-bit segment no. is broken into 8-bit page no. and 10-bit page offset • The segment table is represented by a page table consisting of up to 28 entries 7
- 8. Segmentation with Paging – MULTICS • The logical address in MULTICS is as follows Segment number Offset S1 S2 d1 d2 8 10 6 10 Figure:1 8
- 9. Segmentation with Paging – MULTICS • In fig1 s1 index into the page table of the segment table • s2 is the displacement within the page of the segment table • d1 is a displacement in to the page table of the desired segment • d2 is the displacement into the page containing the word to be accessed 9
- 10. Segmentation with Paging – MULTICS Logical address S1 S2 d1 d2 s1 s2 Page table d1 for segment d1 table Page of segment table Page table for Page of segment segment 10
- 11. MULTICS Address Translation Scheme 11
- 12. Segmentation with Paging – Intel 386 • As shown in the following slide, the Intel 386 uses segmentation with paging for memory management with a two-level paging scheme 12
- 13. Internal architecture of paged segmentation Paged Segmentation Combination of paging and segmentation address = frame at (page table base for segment) + offset into page table + offset into memory Look at example of Intel architecture 13
- 14. Summary In this class, you have learnt • Paged Segmentation 14
- 15. Frequently Asked Questions • What is Paged Segmentation? • Explain the Paged segmentation hardware with a neat diagram ? 15
- 16. Quiz 1. Page no. indexes into the page table to give the a) Segmentation b) Frame no. C) None 2. MULTICS must have a separate page table for each a) Page offset b) Hole c) segment d) None 16
- 17. Quiz 3. ____________ scheme creates a 34-bit address space a) Page number b) MULTICS c) Compaction d) None 17
- 18. Quiz 4. The _________system solved problems of external fragmentation a) External fragmentation b) MULTICS c) Compaction d) None 18
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