366 Chapter 11 File Systems and Directories The SCAN disk-scheduling algorithm works in a similar way, except instead of moving up and down, the read/write heads move in toward the spindle, then out toward the platter edge, then back toward the spindle, and so forth. Let’s perform this algorithm on our set of requests. Unlike the other approaches, though, we need to decide which way the heads are moving initially. Let’s assume they are moving toward the lower cylinder values (and are currently at cylinder 26). As the read/write heads move from cylinder 26 toward cylinder 1, they satisfy the requests at cylinders 22 and 7 (in that order). After reaching cylinder 1, the heads reverse direction and move all the way out to the other extreme. Along the way, they satisfy the following requests, in order: 33, 35, 49, 61, 62, and 91. Note that new requests are not given any special treatment. They may or may not be serviced before earlier requests. It depends on the current location of the heads and direction in which they are moving. If the new
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This note was uploaded on 01/13/2011 for the course CSE 1550 taught by Professor Marianakant during the Fall '10 term at York University.