C scan scheduling 50 2
- 1. C-SCAN Scheduling • C-SCAN Scheduling is a variant of SCAN Scheduling • It is designed to provide uniform wait time • Like SCAN, C-SCAN moves the head from one end of the disk to other end, servicing requests along the way http://raj-os.blogspot.in/ 1
- 2. C-SCAN Scheduling • When the head reaches the other end, – it immediately returns to the beginning of the disk, – without servicing any requests on the return trip • Treats the cylinders as a circular list that wraps around from the last cylinder to the first one http://raj-os.blogspot.in/ 2
- 3. C-SCAN 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/ 3
- 4. C-SCAN Scheduling • If the disk head is initially at cylinder 53, – it will first move from 53 to 65, (towards right) – then to 67, 98, 122, 124, 183,199, 0, 14 and 37 as shown in the next slides http://raj-os.blogspot.in/ 4
- 5. C-SCAN Scheduling Initial head position http://raj-os.blogspot.in/ 5
- 6. C-SCAN Scheduling Head movement from 53 to 65 http://raj-os.blogspot.in/ 6
- 7. C-SCAN Scheduling Head movement from 65th to 67 http://raj-os.blogspot.in/ 7
- 8. C-SCAN Scheduling Head movement from 67 to 98 http://raj-os.blogspot.in/ 8
- 9. C-SCAN Scheduling Head movement from 98 to 122 http://raj-os.blogspot.in/ 9
- 10. C-SCAN Scheduling Head movement from 122 to 124 http://raj-os.blogspot.in/ 10
- 11. C-SCAN Scheduling Head movement from 124 to 183 http://raj-os.blogspot.in/ 11
- 12. C-SCAN Scheduling Head moved to the extreme track http://raj-os.blogspot.in/ 12
- 13. C-SCAN Scheduling Head is moved from one extreme end to the other http://raj-os.blogspot.in/ 13
- 14. C-SCAN Scheduling Head is moving from 0 to 14th track http://raj-os.blogspot.in/ 14
- 15. C-SCAN Scheduling Head is moved from 14th to 37th track http://raj-os.blogspot.in/ 15
- 16. C-SCAN Scheduling • Advantages – Better than SCAN Scheduling in terms of waiting time – i.e., provides uniform waiting time • Disadvantages – It is not optimal http://raj-os.blogspot.in/ 16