The major magnetic storage media are floppy disks and hard disks.
In magnetic disk systems, information is stored as magnetized spots arranged in concentric circles around the disk. These circles are referred to as tracks and are numbered, beginning with 0, from the outside edge inward. The number of tracks may range from 40 up to 2048, depending on the type of disk and drive being used.
In hard disk drives, multiple disks are stacked together on a common spindle. The corresponding tracks of each surface are logically arranged to form a cylinder (i.e., all of the track-0 tracks are taken together to form cylinder-0).
Since the tracks at the outer edge of the disk are longer than those at its center, each track is divided into an equal number of equal-sized blocks called sectors. This arrangement is used so that the logic circuitry for processing data going to, or coming from the disk can be as simple as possible. The number of sectors on a track may range from 8 to more than 60, depending on the disk and drive type, and the operating system software used to format it.
As an example, a typicalIBMfloppy disk will have 40 or 80 tracks per surface, with each track divided into 8, 9, or 18 sectors each. In a PC-compatible system each sector holds 512 bytes of data.
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