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:
“Today, San Francisco has experienced a double tragedy of incredible proportions. As acting mayor, I order an immediate state of mourning in our city. The city and county of San Francisco must and will pull itself together at this time. We will carry on as best as we possibly can.... I think we all have to share the same sense of shame and the same sense of outrage.”
—Dianne Feinstein (b. 1933)