Degaussing magnetic data storage media

Data is stored in the magnetic media, such as hard drives, floppy disks and magnetic tape, by making very small areas called magnetic domains change their magnetic alignment to be in the direction of an applied magnetic field. This phenomenon occurs in much the same way a compass needle points in the direction of the earth's magnetic field. Degaussing, commonly called erasure, leaves the domains in random patterns with no preference to orientation, thereby rendering previous data unrecoverable. There are some domains whose magnetic alignment is not randomized after degaussing. The information these domains represent is commonly called magnetic remanence since it is due to remanent magnetization. Proper degaussing will ensure there is insufficient magnetic remanence to reconstruct the data.

Erasure via degaussing may be accomplished in two ways: in AC erasure, the medium is degaussed by applying an alternating field that is reduced in amplitude over time from an initial high value (i.e., AC powered); in DC erasure, the medium is saturated by applying a unidirectional field (i.e., DC powered or by employing a permanent magnet).