magnetic disk

views updated

magnetic disk A rotatable storage medium usually in the form of a circular nonmagnetic rigid plate coated on both sides with magnetic material, followed by some form of lubricating layer(s). The disks themselves (the substrate) are made of aluminum alloy or of some glass–ceramic composite material. The magnetic coating on early disks was a ferric oxide in a binder. Current disks have a thin metallic film, such as cobalt/nickel or cobalt/chrome, which is created by vacuum deposition (i.e. sputtering). The lubricating layer is a coat of carbon a few angstroms thick, sometimes followed by a proprietary lubricant. Metallic coatings have advantages in being homogeneous, having a better hysteresis loop shape, and allowing storage densities 10 times that achievable with conventional ferric oxide coatings. Flexible magnetic disks (i.e. floppy disks) with oxide coating provide low-cost lightweight media that can be handled in a normal office environment.

Data is stored on and retrieved from magnetic disks by means of a disk drive. See also access time, fixed disk drive, Winchester technology, memory hierarchy.

More From encyclopedia.com