audio. First released in Japan in October 1982, the CD was the second optical disc format to reach the market, following the larger LaserDisc (LD). In later years, the technology was adapted for computer data storage as CD-ROM and subsequently expanded into various writable and multimedia formats. as of 2007, over 200 billion CDs (including audio CDs, CD-ROMs, and CD-Rs) had been sold worldwide.

Standard CDs