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Eight-to-fourteen modulation (EFM) is a data encoding technique invented by Kees A. Schouhamer Immink, which makes CDs and Hi-MD MiniDiscs highly resilient to dust, fingerprints and tiny scratches. Prior to the creation of this data encoding technique, these imperfections negatively affected retrieved data.
Eight-to-fourteen modulation modifies binary code data and allows 17 bits of data space to be used to encode 8 bits of data. The 8-bit block of data is replaced by a 14-bit codeword using a lookup table. This requires more space for data, but assures that imperfections and foreign material do not cause critical data to be missed by the optical pickup in the playback mechanism. This involves two extra zeros placed between two consecutive ones (Ten consecutive zeros are the maximum allowed between consecutive zeros.) Consistently applied, the data can be read accurately even with the disc imperfections and foreign material present. For DVDs and SACDs, a channel code called EFMPlus is used, which translates 8-bit words into 16-bit code words. This results in a 6.25 percent increase in storage capacity above that achieved by classic EFM.