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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.
CD-ROM drives are rated with a speed factor relative to music CDs. If a CD-ROM is read at the same rotational speed as an audio CD, the data transfer rate is 150 Kbyte/s, commonly called "1×" (with constant linear velocity, short "CLV"). At this data rate, the track moves along under the laser spot at about 1.2 m/s.
In later years, the compact disc was adapted for non-audio computer data storage purposes as CD-ROM and its derivatives. First released in Japan in October 1982, the CD was the second optical disc technology to be invented, after the much larger LaserDisc (LD). By 2007, 200 billion CDs (including audio CDs, CD-ROMs and CD-Rs) had been sold ...
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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.
CD-R and CD-RW discs use a frequency modulated wobble of 140.6 kHz to encode information, such as the Absolute Time in Pregroove (ATIP), into the groove. [1] DVD-R and DVD-RW have a constant wobble frequency of 140.6 kHz relying on data 'pits' beside the groove to convey information (Land pre-pit). [2]
This format saw little use. Continual improvements in drive and media led to the 1997 addition of the CD-RW format, which allowed disks to be written, erased and re-written. This format is incompatible with older CD drives, like CD-R, but read-only drives capable of reading CD-RW became common in the 2000s as CD-RW use proliferated.
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.