Double density

Double density

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.


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  • Double Density —   [dt. »doppelte Dichte«], Diskette …   Universal-Lexikon

  • double-density — doubˈle densˈity adjective (computing) (of a disk) capable of recording double the normal number of bytes • • • Main Entry: ↑double * * * ˌdouble ˈdensity 7 [double density] adjective ( …   Useful english dictionary

  • Double Density — 3,5 DD Diskette 5,25 DD Diskette …   Deutsch Wikipedia

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  • double-density — UK / US adjective computing a double density disk holds twice the amount of information as a standard disk …   English dictionary

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  • Double Density Compact Disc — (DDCD) is an optical disc technology developed by Sony using the same laser wave length as compact disc, namely 780 nm. The format is defined by the purple book standard document.For 120 mm disc radius, it doubles the original 650 MB to 1.3 GB… …   Wikipedia

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