Audiopedia

In computing, sound reproduction, and video, an optical disc is a flat, circular disc (usually polycarbonate) wherein data is 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 is 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.

The optical disc was invented in 1958. 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.

NOTE: other factors affecting data storage density are, for example, a multi-layered infrared disc would hold more data than an identical single-layer disc; whether CAV, CLV, or zoned-CAV; how the data are encoded; how much clear margin at the center and the edge

  * Compact Disc (CD)
  * Laser disc
  * Magneto-optical disc
      o mini disc

Second-generation

Second-generation optical discs were for storing great amounts of data, including broadcast-quality digital video. Such discs usually are read with a visible-light laser (usually red); the shorter wavelength and greater numerical aperture allow a narrower light beam, permitting smaller pits and lands in the disc. In the DVD format, this allows 4.7GB storage on a standard 12cm, single-sided, single-layer disc; alternately, smaller media, such as the MiniDisc and the DataPlay formats, can have capacity comparable to that of the larger, standard compact 12cm disc.

  * Hi-MD
  * DVD and derivatives
      o DVD-Audio
      o DualDisc
      o Digital Video Express (DIVX)
  * Super Audio CD
  * Video CD
  * Super Video CD
  * Enhanced Versatile Disc
  * GD-ROM
  * DataPlay
  * Phase-change Dual
  * Universal Media Disc
  * Ultra Density Optical

Third-generation

Third-generation optical discs are in development, meant for distributing high-definition video and support greater data storage capacities, accomplished with short-wavelength visible-light lasers and greater numerical apertures. The Blu ray disc uses blue-violet lasers of greater aperture, for use with discs with smaller pits and lands, thereby greater data storage capacity per layer.  In practice, the effective multimedia presentation capacity is improved with enhanced video data compression codecs such as H.264, and VC-1.

  * Currently shipping:
      o Blu ray Disc
      o HD VMD Disc
      o CBHD Disc

  * In development:
      o Forward Versatile Disc
      o Digital Multilayer Disk or Fluorescent Multilayer Disc

  * Abandoned:
      o HD DVD

Next generation

The following formats are ahead of current (third-generation) discs, having the potential more than one terabyte (1TB) of data storage space.

  * Holographic Versatile Disc
  * LS-R
  * Protein-coated disc