In magnetic and optical storage media, a sector is understood to be the smallest addressable storage units. The sectors are defined storage areas within the tracks, which are applied as concentric circles on the storage media.
In the case of hard disks and floppy disks, 512 data bytes can be stored in a sector. Depending on whether the tracks are outside or inside, they have a different number of sectors. For hard disks, the number of sectors per track is between 50 and 200.
The memory block used by operating systems is usually much larger than the memory area of a sector. The data from several sectors is combined to form a cluster, which is addressed via a unique number.
In the case of compact discs( CD), a sector contains a different number of data and control frames. For example, a sector on the CD-DA contains 98 audio frames; on the CD-ROM, a sector has 2,352 bytes, with 98 audio frames integrated in such a sector.
Whereas in the past the sectoring of floppy disks was still defined in the form of hard-sectoring, later storage media were soft-sectored.