Disk Scheduling Q1. Suppose a disk has 201 cylinders, numbered from 0 to 200. At some time the disk arm is atcylinder 100, and there is a queue of disk access requests for cylinders 30, 85, 90, 100, 105, 110,135 and 145. If Shortest-Seek Time First (SSTF) is being used for scheduling the disk access, therequest for cylinder 90 is serviced after servicing ____________ number of requests.Q2. Consider an operating system capable of loading and executing a single sequential userprocess at a time. The disk head scheduling algorithm used is First Come First Served (FCFS). IfFCFS is replaced by Shortest Seek Time First (SSTF), claimed by the vendor to give 50% betterbenchmark results, what is the expected improvement in the I/O performance of user programs?Q3. Suppose the following disk request sequence (track numbers) for a disk with 100 tracks isgiven: 45, 20, 90, 10, 50, 60, 80, 25, 70. Assume that the initial position of the R/W head is ontrack 50. The additional distance that will be traversed by the R/W head when the Shortest SeekTime First (SSTF) algorithm is used compared to the SCAN (Elevator) algorithm (assuming thatSCAN algorithm moves towards 100 when it starts execution) is _________ tracks Q4. Consider a typical disk that rotates at 15000 rotations per minute (RPM) and has a transferrate of 50 × 106bytes/sec. If the average seek time of the disk is twice the average rotationaldelay and the controller’s transfer time is 10 times the disk transfer time, the average time (inmilliseconds) to read or write a 512 byte sector of the disk is _____________ Page replacement Algorithms
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- Spring '19
- Omprakash Patel
- Virtual memory, Page replacement algorithm