COMP3511-hw4-Spring 2018(sol)(updated).docx

# Note in the last replacement there is insufficient

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Note: in the last replacement, there is insufficient future frames to refer to for decision making in OPTIMAL method, can either use LRU, or FIFO for this last page replacement.since they have similar number of page faults. i.e. either 2301 or 2314 are correct for this last page replacement. Page faults: 8 2) If delta = 6, what is the working set at the point t as shown: 2, 0, 1, 4, 0, 5, 2, 4, 0, 2, 3, 4, 2, 5, 0, 4, 1, 3, 2, 1 (8 points) Answer: working set = {0, 1, 2, 4, 5} 4. (10 points)Consider a UNIX file system that uses inodes to represent files. The logical address has 32 bits, and disk block size is 4KB. The combined scheme is used for disk allocation, with 10 direct disk blocks, plus one single, one double, and one triple indirect disk blocks. What is the maximum file size that can be supported in this file system? Answer: With a 32-bit address, each pointer needs 32 bit or 4 bytes. So one block with 4KB has 1024 pointers (2 points). The maximum file size is 10x4KB + 1024x4KB+1024x1024x4KB + 1024x1024x1024x4KB = 4TB (approximately) 5. (20 points) Disk scheduling problem Suppose that a disk drive has 200 cylinders, numbered 0 to 199. The drive is currently serving a request at cylinder 100, and the previous request was at cylinder 20. The queue of pending requests, in FIFO order, is: 55 58 39 18 90 160 150 38 184 Starting from the current head position (100), what is the average distance (in cylinders) that the disk arm moves to satisfy all the pending requests for each of the following disk-scheduling algorithms? a) FCFS b) SSTF c) SCAN 5 t

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d) C-SCAN e) LOOK f) C-LOOK Answer: The FCFS schedule is 55, 58, 39, 18, 90, 160, 150, 38, 184. The average seek distance is 55.3. (498/9) The SSTF schedule is 90, 58 ,55, 39, 38, 18, 150, 160, 184. The average seek distance is 27.6. (248/9) The SCAN schedule is 150, 160, 184,(199), 90, 58, 55, 39, 38, 18. The average seek distance is 31.3. (280/9) The C-SCAN schedule is 150, 160, 184, (199), (0), 18, 38, 39, 55, 58, 90. The average seek distance is 43.1. (388/9) The LOOK schedule is 150, 160, 184, 90, 58, 55, 39, 38, 18. The average seek distance is 27.8. (250/9) The C-LOOK schedule is 150, 160, 184, 18, 38, 39, 55, 58, 90. The total seek distance is 35.8. (322/9) 6
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• Fall '14
• page faults, average seek distance

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