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Eight-to-Fourteen Modulation, or EFM as it is abbreviated, is an encoding technique used by CDs and provides a way of countering errors by encoding a byte into 2 bytes. Using EFM the data is broken into 8-bit blocks (bytes). Each 8-bit block is translated into a corresponding 14-bit codeword using a predefined lookup table. The 14-bit codeword are chosen so that binary ones are always separated by a minimum of two and a maximum of ten binary zeroes. EFM maximizes the number of transitions possible with an arbitrary pit and land length which is determined by the wavelength of the laser light used to read the data. Eight-to-Fourteen Modulation uses an RLL encoding scheme.
