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A CD-ROM (/ ˌ s iː d iː ˈ r ɒ m /, ... Data is stored on the disc as a series of microscopic indentations called "pits", with the non-indented spaces between ...
The pit geometry and quality of the playback can all be adjusted while the CD is being mastered, as the blue writing laser and the red read laser are typically connected via a feedback system to optimise the recording. This allows the dye-polymer LBR to produce very consistent pits even if there are variations in the dye-polymer layer.
For the first few years of its existence, the CD was a medium used purely for audio. In 1988, the Yellow Book CD-ROM standard was established by Sony and Philips, which defined a non-volatile optical data computer data storage medium using the same physical format as audio compact discs, readable by a computer with a CD-ROM drive.
For a 12 cm disc, it doubles the original 650 MB to 1.3 GB capacity of a CD on recordable (DDCD-R) and rewritable (DDCD-RW) discs by narrowing the track pitch from 1.6 to 1.1 micrometers, and shortening the minimum pit length from 0.833 to 0.623 micrometers. The DDCD was also available in read-only format (DDCD-ROM).
Dimensions indicated are track pitch (p), pit width (w) and minimum length (l), and laser spot size (⌀) and wavelength (λ). For comparison with analogue media, the pitch of the spiral of a 240-groove-per-inch long-playing record and a Laserdisc are 106 μm (66 times the CD track pitch) and 4.6 μm (2.9 times), respectively.
The preservation of optical media is essential because it is a resource in libraries, and stores audio, video, and computer data. While optical discs are generally more reliable and durable than older media types, (magnetic tape, LPs and other records) environmental conditions and/or poor handling can result in lost information.
The latest editions have abandoned the use of the term CD-WO in favor of CD-R, while CD-MO was rarely used. Written CD-Rs and CD-RWs are, in the aspect of low-level encoding and data format, fully compatible with the audio CD (Red Book CD-DA) and data CD (Yellow Book CD-ROM) standards. The Yellow Book standard for CD-ROM only specifies a high ...
Eight-to-fourteen modulation (EFM) is a data encoding technique – formally, a line code – used by compact discs (CD), laserdiscs (LD) and pre-Hi-MD MiniDiscs. EFMPlus is a related code, used in DVDs and Super Audio CDs (SACDs). EFM and EFMPlus were both invented by Kees A. Schouhamer Immink.