Disk storage is a general category of storage mechanisms where data are recorded by various electronic, magnetic, optical, or mechanical changes to a surface layer of one or more rotating disks. A
disk drive is a device implementing such a storage mechanism. Notable types are the
hard disk drive (HDD) containing a non-removable disk, the
floppy disk drive (FDD) and its removable
floppy disk, and various
optical disc drives and associated
optical disc media.