Magnetic recording encoder system for A(1,7) channel having a 2/3 coding rate

An improvement in a system for encoding a data field (12) on a disk with write gate data (15). The system (10) has an encoder (16) and a data receiving controller for directing write gate data (15) in the form of 0 and 1 bits to the encoder. The encoder (16), in response to the write gate data (15), produces a primary code in the form of 0 and 1 bits and directing the primary code to the disk. The primary code has certain predetermined criteria with the encoder producing a secondary coding rate as an exception when the write gate data does not result in the predetermined criteria. The improvement comprises a mechanism for ensuring that the last predetermined number of bits in the data field are free from the exception.