Double-density compact disc (DDCD) is an optical disc technology developed by Sony using the same laser wavelength as compact disc, namely 780 nm. The format is defined by the Purple Book standard document.
For a 120 mm disc, it doubles the original 650 MB to 1.3 GB capacity of a CD on recordable (DDCD-R) and rewritable (DDCD-RW) discs by narrowing the track pitch from 1.6 to 1.1 micrometers, and shortening the minimum pit length from 0.833 to 0.623 micrometer. The DDCD was also available in read-only format (DDCD-ROM). All three formats existed also in small 80 mm discs.
The technology failed to acquire significant market share before the success of DVD technology. The DVD technology offered a significantly higher capacity (four times more initially with 4.7 GB on single layer discs, 8.5 GB on dual layer discs to a max of 17.08GB on a dual-side+dual layer disc).
The only DDCD recorder introduced was the Sony CRX200E.
The technology was marked as 'legacy' in the 2006-edition of the SCSI Multimedia Commands set (MMC).