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:
“I grew up confidently expecting to have a profession and earn my own living, and also confidently expecting to be married and have children. It was fifty-fifty with me. I was just as passionately determined to have children as I was to have a career. And my mother was the triumphant answer to all doubts as to the success of this double role. From my earliest memory she had more than half supported the family and yet she was supremely a mother.”
—Crystal Eastman (1881–1928)