eight to fourteen modulation (CD, DVD) (EFM)
Eight to Fourteen Modulation(EFM) is an encoding used on Compact Discs ( CD) and Digital Versatile Discs( DVD) that ensures higher storage density and flawless reading of the storage medium.
In the EFM process, 8 bits are converted into a bit pattern of 14 bits, with a minimum of three and a maximum of eleven zeros between the two ones. Fourteen bits are required for this concept, in which a byte with its 256 possible combinations is represented without two ones following each other.
The EFM method is implemented in CD drives. A variant of this method is EFM-Plus (EFM+), which is used in DVDs and uses 16-bit words and low frequency suppression for increased data security. EFM-Plus has 3 control bits per byte.