In computing, sound reproduction, and video, an optical disc is a flat, circular disc (usually polycarbonate) wherein data are stored in the pits (or bumps) in its flat surface — sequentially on the continuous, spiral track extending from the innermost track to the outermost track, covering the entire disc surface. The data are accessed in the disc when a special material (often aluminium) is illuminated with a laser diode. The pits distort the reflected laser light, hence, most optical discs (except the black discs of the original PlayStation video game console), characteristically have an iridescent appearance created by the grooves of the reflective layer.

Write-once optical discs commonly use an organic dye, and re-writable discs use phase change alloys.

History

In 1961 and 1969, David Paul Gregg registered a patent for the analog optical disc for video recording, (US Patent 3,430,966). It is of special interest that US Patent 4,893,297, filed 1968, issued 1990, generated royalty income for Pioneer Corporation's DVA until 2007 — encompassing the CD, DVD, and Blu-ray disc systems. In the early 1960s, the Music Corporation of America bought Gregg's patents and his company, Gauss Electrophysics.

Likewise, in 1969 Holland, Philips Research physicists began their first optical videodisc experiments at Eindhoven. In 1975, Philips and MCA join efforts, and in 1978, commercially much too late, they presented their long-awaited laserdisc in Atlanta, Georgia, USA MCA delivered the discs, Philips the players; the presentation was a technical and commercial failure; the Philips/MCA cooperation ended.

In Japan and the U.S., Pioneer succeeded with the videodisc until the advent of the DVD. In 1979, Philips and Sony, in consortium, successfully developed the compact disc in 1983. The Optical Storage Technology Association (OSTA) promote standardised optical storage means. Although optical discs are more durable than earlier audio-visual and data storage formats, they are susceptible to environmental and daily-use damage. Libraries and archives enact optical media preservation procedures to ensure continued usability in the computer's optical disc drive or corresponding disc player.

First-generation

Initially, optical discs were for storing music and computer software. The laser disc format stored analog video signals, but, commercially, lost to the VHS videotape cassette, mainly its high cost and non-recordability; other first-generation disc formats are designed solely to store digital data.

Most first-generation disc devices had an infrared laser reading head. The minimum size of the laser spot is proportional to its wavelength, thus wavelength is a limiting factor against great information density, too little data can be stored so. The infrared range is beyond the long-wavelength end of the visible light spectrum, so, supports less density than any visible light colour. One example of high-density data storage capacity, achieved with an infrared laser, is 700MB of net user data for a 12cm compact disc.