Disk storage can be anything from a CD ROM to a floppy disk or Hard disk. The general term for any physical storage unit is volume. Disks are divided in tracks, these tracks are not a physical division as on a record and their position is fixed by the Read/Write head. The tracks are numbered, then subdivided into sectors. Sectors are normally the same size on each track and throughout the disk, sectors are numbered by inserting the sector number into the sector header.