Why is FCFS scheduling an acceptable solution for disk scheduling in a single-us
ID: 3819499 • Letter: W
Question
Why is FCFS scheduling an acceptable solution for disk scheduling in a single-user environment? Explain your answer In SSTF scheduling, the algorithm tends to favor middle cylinders over the innermost and outermost cylinders. Why is this the case? Suppose that a disk drive has 5, 000 cylinders, numbered 0 to 4999. The drive is currently serving a request at cylinder 2150, and the previous request was at cylinder 1805. The queue of pending requests, in FIFO order, is: 2063, 1215, 2290, 2808, 547, 1613, 351, 1528, 4960, and 3687. Starting from the current head position, give the order of service requests and the total 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 d. LOOK e. C-SCAN f. C-LOOKExplanation / Answer
1. Why FCFS scheduling ?
In a single-user environments , the I/O queue usually empty for more time. Request generally arrive from a single process or single user for one block or for a sequence of consecutive blocks. In these cases, FCFS is an acceptable solution for disk scheduling method in single user environment..
2. In SSTF why algorithm favor middle cylinder more ?
Center of the disk is the perfect location, having the smallest average distance from all other tracks. Thats why the disk head tend to move away from the edges of the disks. The current location of the head divide the cylinders into two groups of cylinders. If head is not in the center of the disk and a new request arrives, the
new request is more likely to be in the group that includes the center of the disk; thus, the head is more likely to move in that direction. thats why SSTF favors middle cylinders more then outermost and innermost cylinders.
3. Order of Service Requests are :
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