AlgoPlus//structures / disk-scheduling
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Disk Scheduling

The head seeks across cylinders — the policy orders requests to minimise total travel.

Policy
SSTF
Head movement
0
Serviced
0/8
Policy
Request queue (cylinders 0–199)
Legend
Head path / current
Serviced request
Pending request
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In a nutshell
Reaching data on a spinning disk means moving the read/write head to the right cylinder, and that travel — the seek time — is the slow part. The scheduling policy reorders the pending requests to cut total head movement: FCFS serves them in arrival order, SSTF jumps to the nearest, and SCAN/LOOK sweep across the disk like an elevator. Less head travel means faster service.
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Seeking is the slow part of a disk, so the order you service requests matters. SSTF and the elevator-style SCAN/LOOK family cut total head travel versus first-come-first-served — at the cost of fairness (SSTF can starve far requests; C-SCAN evens it out).
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