Optical disc

A piece of optical media, a round disc (e.g. a Compact Disc, Digital Versatile Disc, or Laserdisc), used as powerless persistent memory storage. Though special chemicals and techniques can be used to make rewritable optical media, most are read-only.

Overview
Optical discs are read in a hardware drive with three key mechanisms: a rotating spindle the disc is mounted on, a laser that is projected onto the disc and reflected back (into a sensor in the same assembly), and an arm that the laser itself is on, which can move back and forth. Thus, by spinning the disc and adjusting the arm, the drive can use the laser to access any part of the disc. Data is interpreted as bits depending on how the laser reflects, which in turn depends on indentations in the media.

Developing generations of optical media use finer and finer indentations and more accurate lasers to make the information itself physically denser.

A relatively new technology is the dual-layer HD DVD. The different layers are accessed by the laser being focused for the different layers and increasing or decreasing intensity of the laser to read or bypass the translucent first layer.

The latest generation is Blu-Ray.

History of optical disc technology

 * Continuous wave semiconductor laser
 * Invented by Izuo Hayashi and Morton B. Panish in 1970. This led directly to the light sources in fiber-optic communication, laser printer, barcode readers, and optical disc drives, technologies that were commercialized by Japanese entrepreneurs.


 * Holographic data storage
 * In 1975, Hitachi introduced a video disc system in which chrominance, luminance and sound information were encoded holographic. Each frame was recorded as a 1mm diameter hologram on a 305mm disc, while a laser beam read out the hologram from three angles.


 * Compact Disc (CD)
 * The compact disc was developed by Sony (Toshitada Doi). Sony first publicly demonstrated an optical digital audio disc in September 1976. In September 1978, they demonstrated an optical digital audio disc with a 150 minute playing time, and with specifications of 44,056 Hz sampling rate, 16-bit linear resolution, cross-interleaved error correction code, that were similar to those of the Compact Disc they introduced in 1982.


 * Compact Disc Digital Audio (CD-DA)
 * Also called Red Book, CD-DA was the compact disc audio format introduced in 1980 by Sony and Philips.


 * CD-ROM
 * The CD-ROM format was developed by Japanese company Denon in 1982. It was an extension of Compact Disc Digital Audio, and adapted the format to hold any form of digital data, with a storage capacity of 553 MiB. CD-ROM was then introduced by Denon and Sony at a Japanese computer show in 1984.


 * Laserdisc digital data storage
 * In 1984, Sony introduced a laserdisc format that could store any form of digital data, as a data storage device similar to CD-ROM, with a larger capacity of 3.28 GiB.


 * Digital video disc (DVD)
 * The DVD, first developed in 1995, was created by three Japanese companies: Sony, Toshiba, and Panasonic.


 * Blu-ray Disc
 * After Shuji Nakamura's invention of practical blue laser diodes, Sony started two projects applying the new diodes: UDO (Ultra Density Optical) and DVR Blue (together with Pioneer), a format of rewritable discs which would eventually become the Blu-ray Disc. The Blu-ray Disc Association was founded by five companies from Japan and two from South Korea.

History of optical discs in video games
The first video game to use optical disc storage was SEGA's Astron Belt, the first laserdisc video game. It was first demonstrated in 1982 and released for arcades in early 1983.

The first video game system to use CD-ROM storage was the PC-Engine CD-ROM² console, released in Japan in 1988 and then released as the TurboGrafx-CD in North America in 1989.

The first video game system to use DVD storage was the PlayStation 2, released in 2000. The first video game system to use Blu-Ray storage was the PlayStation 3, released in 2006.