Disk

Disk, in computer science, a round, flat piece of flexible plastic (floppy disk) or inflexible metal (hard disk) coated with a magnetic material that can be electrically influenced to hold information recorded in digital (binary) form. A disk is, in most computers, the primary means of storing data on a permanent or semipermanent basis. Because the magnetic coating of the disk must be protected from damage or contamination, a floppy (5.25-inch) disk or microfloppy (3.5-inch) disk is encased in a protective plastic jacket. A hard disk, which is very finely machined, is enclosed in a rigid case and can be exposed only in a dust-free environment. Standard floppy and microfloppy disk designs are being phased out in favor of compact discs (CD-ROMs), and new microfloppy designs with upward of one hundred times the storage capacity of their older counterparts. Users cannot record information on CD-ROMs, but recordable compact discs (CD-Rs) and rewriteable compact disks (CD-RWs) are becoming widespread. A hybrid of the optical storage techniques used in CD-ROMs and the magnetic storage capabilities of floppy disks, called a floptical or magneto-optical disk, provides large storage capacities and the option to read and write information upon them. See also Computer; Microfloppy Disk; Storage.