39 virtual memory
- 1. Storage Management • Virtual Memory 1
- 2. HOME PREVIOUS TOPIC NEXT PREVIOUS QUESTION PAPERS FOR OS CPP TUTORIALS 9CM402.39 2
- 3. Recap In the last class, you have learnt: • Paged Segmentation • MULTICS Address Translation Scheme 3
- 4. Objective On completion of this class, you will be able to know • Virtual Memory Techniques 4
- 5. Virtual Memory Techniques • RAM is expensive ( but fast ), disk is cheap (but slow) • Need to find a way to use the cheaper memory – Store memory that isn’t frequently used on disk – Swap pages between disk and memory as needed • Treat main memory as a cache for pages on disk 5
- 6. Virtual Memory • It is separation of user logical memory from physical memory – Only part of the program needs to be in memory for execution – Logical address space can therefore be much larger than physical address space – Allows address spaces to be shared by several processes – Allows for more efficient process creation 6
- 7. Virtual Memory • Virtual memory can be implemented via: – Demand paging – Demand segmentation 7
- 8. Virtual Memory • It is a conceptual separation of user logical memory from physical memory • Thus we can have large virtual memory on a small physical memory Individual Pages Physical Disk Virtual Memory Memory Map Memory 8
- 9. Virtual Memory • Programs can be larger than memory – Program loaded into memory as needed – Active program and data “swapped” to a disk until needed • Memory space treated uniformly 9
- 10. WHY VIRTUAL MEMORY? • Previously entire logical space was required for the process to be in memory • Before the process could run • The alternatives to this • Most code / data isn't needed at any instant, or even within a finite time • We can bring it in only as needed 10
- 11. Virtual Memory Advantages • Gives a higher level of multiprogramming • The program size isn't constrained (thus the term 'virtual memory'). Virtual memory allows very large logical address spaces • Swap sizes smaller 11
- 12. Summary In this class, you have learnt • Virtual Memory 12
- 13. Frequently Asked Questions • Explain Virtual Memory concepts with a neat sketch 13
- 14. Quiz 1. __________separation of user logical memory from physical memory a) Segmentation b) Virtual memory c) None 2. ____________gives a higher level of multiprogramming a) Page offset b) Hole c) Virtual memory d) None 14
- 15. Quiz 3. Logical address space can be much larger than a) Page number b) MULTICS c) Physical address space d) None 4. __________allows very large logical address spaces a) External fragmentation b) Virtual memory c) Compaction d) None 15
- 16. Other subject materials • Web designing • Micro processors • C++ tutorials • java home