cylinder

Definition: (1) A set of tracks on a floppy disk or hard-disk that are in the same relative positions on opposite sides of the disk or platter. * In hard-disks which consist of several platters, a cylinder comprises all the tracks with the same numbers on all sides of all disks. * Cylinder information is important for correctly setting up a hard disks but rarely concern the user. (2) Axis used to define astigmatism in an eye. * The cylinder axis is the principal meridian of the lower focal length of an astigmatic lens.

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