Compact discs use a special format to encode digital data. There is not a direct cor-
relation between a “bit” and a “pit” in optical storage. Optical drive optics are not
sufficiently precise to read and interpret each individual “pit” as a bit. Laser beams
are focused into a spot of about 1 micron in diameter so they can miss pits that are
.83 microns wide. The solution was to devise a coding scheme that bundles user
data with error correction and synchronization data into a symbol called a channel
bit. Laser beams read transitions between these symbols. CD drives include code to
interpret these channel bits on playb ...
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