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:
“The Cossack eats Poland,
Like stolen fruit;
Her last noble is ruined,
Her last poet mute:
Straight, into double band
The victors divide;
Half for freedom strike and stand;—
The astonished Muse finds thousands at her side.”
—Ralph Waldo Emerson (1803–1882)