Optical disk

Description

A plastic or glass disk used as an optical storage medium for digital data, such as music, images, or text. An analog optical disk for video images was first developed by David Gregg in 1961 (patent date). The most common optical disk is called a Compact disc (CD). CD's were first used as audio storage media that could hold up to 74 minutes of high fidelity sound. Later developments created computer readable CD's for storage of up to 680 megabytes of data, images and software. Other varieties of optical disks include early laserdiscs and the more recent digital videodiscs (DVD).

For all optical disks, the hard thin substrate, such as polycarbonate, is coated with a reflective aluminum layer that is protected with a thin acrylic lacquer. In read only memory CD's (i.e. CD-ROM and audio CD's), the data layer is pressed into the plastic by a stamper during the injection molding process. The digital pattern is read by a laser scanning the imprinted surface then monitoring the variations in the reflected laser beam. For recordable CD's, a thin layer of a transparent organic dye covers the reflective metallic layer. The recording laser selectively melts pits in the dye to make it opaque and thus the reading laser will not be reflected back in these regions.

Synonyms and Related Terms

CD-ROM; compact disc; optical disc; laserdisc; videodisc; digital versatile disc; digital videodisc; DVD; optische schijf (Ned.); disque optique (Fr.); optischer Plattenspeicher (Deut.); optische Speicherplatte (Deut.); disco a lettura ottica (It.); disco ottico (It.); disco óptico (Esp.); optisk skiva (Svend.)

Resources and Citations

• The American Heritage Dictionary or Encarta, via Microsoft Bookshelf 98, Microsoft Corp., 1998

• Encyclopedia Britannica, http://www.britannica.com Comment: "optical storage." Accessed 15 Mar. 2005 .

• Multilingual Glossary for Art Librarians at http://www.ifla.org/VII/s30/pub/mgl.htm

• Wikipedia: http://en.wikipedia.org/wiki/Optical_disk (Accessed Feb. 2, 2006)