View image The arrangement and organisation of the tracks on a disk. Each track is divided into a number of equal-length blocks, called sectors. A sector is the smallest addressable portion of a track and is the smallest unit of data that is written to or read from a disk. Normally each sector on each track holds the same amount of data, even though outer tracks are longer than inner tracks, so the packing density depends upon the distance of the track from the centre of the disk. Some disk systems use variable speed disks which have different amounts of data on each track. A disk formatted for one operating system cannot normally be used in a different operating system.