Elevator algorithm

The elevator algorithm, or SCAN, is a disk-scheduling algorithm to determine the motion of the disk's arm and head in servicing read and write requests.

This algorithm is named after the behavior of a building elevator, 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.

From an implementation perspective, the drive maintains a buffer of pending read/write requests, along with the associated cylinder 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.

The algorithm is largely obsolete for data storage. With the current generation of magnetic disks it is not possible to know the location of specific data on the disk and solid state memory devices have a constant seek time independent of location.

Schach, Stephen (1996). Classical and Object-Oriented Software Engineering (3rd ed.). Irwin. p. 240. ISBN 978-0-256-18298-9.

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