A Compact Disc or CD is an optical disc meant to store digital data, initially developed for storing digital audio. The CD, obtainable on the market in late 1982, remains the standard physical medium for commercial audio recordings as of 2007. An audio CD includes one or more stereo tracks stored using 16-bit PCM coding at a sampling rate of 44.1 kHz. Standard CDs include a diameter of 120 mm and can hold about 80 minutes of audio. There are also 80 mm discs, occasionally used for CD singles, which hold around 20 minutes of audio. Compact Disc technology was afterward modified for use as a data storage device, known as a CD-ROM, and it consist of record-once and re-writable media (CD-R and CD-RW respectively). CD-ROMs and CD-Rs stay widely used technologies in the Computer industry as of 2007.