![Quiz
1. The SSTF Scheduling is based on Minimal seek
time criteria for selection of requests [T/F]
TRUE
2. The SSTF Scheduling may cause starvation of some
requests [T/F]
TRUE
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![Quiz
3. The SCAN Scheduling algorithm is also called
elevator algorithm [T/F]
TRUE
4. The SCAN Scheduling algorithm doesn't provide
uniform wait time
TRUE
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![Quiz
5. C-SCAN Scheduling provides uniform waiting time
than SCAN Scheduling [T/F]
TRUE
6. C-SCAN Scheduling treats the cylinders as a circular
list that wraps around from the last cylinder to the
first one. [T/F]
TRUE
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Sstf scheduling.50
- 1. SSTF, SCAN, C-SCAN algorithms http://raj-os.blogspot.in/ 1
- 2. HOME PREVIOUS TOPIC NEXT PREVIOUS QUESTION PAPERS FOR OS CPP TUTORIALS http://raj-os.blogspot.in/ 2
- 3. Recap In the last class, you have learnt: - Disk scheduling its need – The FCFS disk scheduling algorithm – Advantages – Disadvantages http://raj-os.blogspot.in/ 3
- 4. Objectives On Completion of this period, you would be able to know : • SSTF , SCAN, C-SCAN disk scheduling algorithm • Advantages • Disadvantages http://raj-os.blogspot.in/ 4
- 5. SSTF Scheduling • The Shortest-Seek-Time-First Scheduling – Services the requests at the current head position – Before moving the head far away http://raj-os.blogspot.in/ 5
- 6. SSTF Scheduling • Minimal seek time is the criteria for selection of requests – Seek time is proportional to the track difference between requests – Head is moved to the closest track in the request queue http://raj-os.blogspot.in/ 6
- 7. SSTF Scheduling • Consider for example an ordered disk queue with requests involving – Tracks 98, 183, 37, 122, 14, 124, 65, 67 – Head pointer 53 • The request queue (0-199) http://raj-os.blogspot.in/ 7
- 8. SSTF Scheduling • If the disk head is initially at cylinder 53, – it will first move from 53 to 65, – then to next closest position 67, 37, 14, 98, 122, 124 and 183 as shown in the next slides • The total head movement of 236 tracks http://raj-os.blogspot.in/ 8
- 9. SSTF Scheduling Initial head position http://raj-os.blogspot.in/ 9
- 10. SSTF Scheduling Head movement from 53 to 65th track http://raj-os.blogspot.in/ 10
- 11. SSTF Scheduling Head movement from 65th to 67th track http://raj-os.blogspot.in/ 11
- 12. SSTF Scheduling Head movement from 67th to 37th track http://raj-os.blogspot.in/ 12
- 13. SSTF Scheduling Head movement from 37th track to 14th track http://raj-os.blogspot.in/ 13
- 14. SSTF Scheduling Head movement 14th track to 98th track http://raj-os.blogspot.in/ 14
- 15. SSTF Scheduling Head movement from 98th to 122 track http://raj-os.blogspot.in/ 15
- 16. SSTF Scheduling Head movement from 122 to 124 http://raj-os.blogspot.in/ 16
- 17. SSTF Scheduling Head movement from 124 to 183rd track http://raj-os.blogspot.in/ 17
- 19. SSTF Scheduling Advantages • It is substantial improvement over FCFS • It is a essential form of Shortest Job First Scheduling http://raj-os.blogspot.in/ 19
- 20. SSTF Scheduling Disadvantages • It may cause starvation of some requests • It is not optimal • The total head movement can be further reduced http://raj-os.blogspot.in/ 20
- 21. Summary In this class, you have learnt: • The SSTF, SCAN,C-SCAN Scheduling • Advantages • Disadvantages http://raj-os.blogspot.in/ 21
- 22. Frequently Asked Questions 1. List the advantages and disadvantages of SSTF,SCAN, C-SCAN algorithms 2. Compare SCAN and C-SCAN scheduling algorithm 3. Explain SSTF scheduling algorithm with the help an example 4. Explain SCAN scheduling algorithm with the help an example 5. Explain C-SCAN scheduling algorithm with the help an example http://raj-os.blogspot.in/ 22
- 23. Quiz 1. The SSTF Scheduling is based on Minimal seek time criteria for selection of requests [T/F] TRUE 2. The SSTF Scheduling may cause starvation of some requests [T/F] TRUE http://raj-os.blogspot.in/ 23
- 24. Quiz 3. The SCAN Scheduling algorithm is also called elevator algorithm [T/F] TRUE 4. The SCAN Scheduling algorithm doesn't provide uniform wait time TRUE http://raj-os.blogspot.in/ 24
- 25. Quiz 5. C-SCAN Scheduling provides uniform waiting time than SCAN Scheduling [T/F] TRUE 6. C-SCAN Scheduling treats the cylinders as a circular list that wraps around from the last cylinder to the first one. [T/F] TRUE http://raj-os.blogspot.in/ 25
- 26. Other subject materials • Web designing • Micro processors • C++ tutorials • java home http://raj-os.blogspot.in/ 26