DVD has the same principle in reading and writing in data with CD. The pit and land on the disc is to store information. The pit and land are all read as 0. the length of pit and land shall determine the number of 0.The joint of pit and land is read as 1.If the binary numbers works as channel code without concocting, the laser heads will have difficult in reading and writing in data. When coming up with "10101010" the read-write frequency is high, and the bandwidth of the laser circuit shall be wider, while coming up with "00000000", the read-write frequency is very low and the laser beam shall lose the track rail information. Therefore, CD uses EFM, which is 8-14 modulation technology and 3 bits of segregation code to from a 17 bit channel code. DVD is the 8-16 the use of advanced modulation techniques, without separation code, you can not meet up to have more than 10 continuous 0, at least two consecutive 0 requirements. The formation of the channel code is 16 bit to save one digit compared with CD.