Double density, often shortened DD, is a capacity designation on magnetic storage, usually floppy disks. It describes the use of an encoding (or modulation) of information, which can encode on average twice as many bits per time unit compared to single density. This is achieved by using MFM instead of FM.
Floppy disk drives have been using this method since 1978 with the introduction of the 360 KiB (MS-DOS FAT size) drives.
The early hard disks also used this encoding, but was replaced by the more efficient RLL method.
Famous quotes containing the word double:
“American families, however, without exception, experience a double message in our society, one that claims a commitment to families and stresses the importance of raising bright, stable, productive citizens, yet remains so bound by an ideal of “rugged individualism” that parents receive little support in their task from the public or private sectors.”
—Bernice Weissbourd (20th century)