The smallest unit that can be accessed on a disk. When a disk undergoes a low-level format, it is divided into tracks and sectors. The tracks are concentric circles around the disk and the sectors are segments within each circle. For example, a formatted disk might have 40 tracks, with each track divided into 10 sectors. The operating system and disk drive keep tabs on where information is stored on the disk by noting its track and sector number.
Modern hard disk drives use a technique called zoned-bit recording in which tracks on the outside of the disk contain more sectors than those on the inside.
A sector that cannot be used due to a physical flaw on the disk is called a bad sector.
