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Elevator algorithm
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<p>The elevator algorithm, or SCAN, is a <a href="/facts/Hard_disk/kekLSGSE">disk</a>-<a href="/facts/I/O_scheduling/4WvHrePc">scheduling</a> algorithm to determine the motion of the disk's arm and head in servicing read and write requests. </p><p>This algorithm is named after the behavior of a building <a href="/facts/Elevator/ug3nh0o8">elevator</a>, where the elevator continues to travel in its current direction (up or down) until empty, stopping only to let individuals off or to pick up new individuals heading in the same direction. </p><p>From an implementation perspective, the <a href="/facts/Disk_drive/hnsXRb5X">drive</a> maintains a <a href="/facts/Data_buffer/tVy4j2Dc">buffer</a> of pending read/write requests, along with the associated <a href="/facts/Cylinder_(disk_drive)/rUMqWXob">cylinder</a> number of the request, in which lower cylinder numbers generally indicate that the cylinder is closer to the spindle, and higher numbers indicate the cylinder is farther away. </p>