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:
“In a symbol there is concealment and yet revelation: here therefore, by silence and by speech acting together, comes a double significance.... In the symbol proper, what we can call a symbol, there is ever, more or less distinctly and directly, some embodiment and revelation of the Infinite; the Infinite is made to blend itself with the Finite, to stand visible, and as it were, attainable there. By symbols, accordingly, is man guided and commanded, made happy, made wretched.”
—Thomas Carlyle (1795–1881)