Five runlength-limited codes for M-ary recording channels

This paper is concerned with M-ary runlength-limited (RLL) codes for nonbinary recording channels. The codes have fixed-rate finite state encoders, sliding block decoders, and large coding density. Five codes are given achieving coding densities of 24 bit/minimum-recorded-mark as compared with 1-1.5 for binary recording channels. The codes are 93-98.5% efficient and either achieve or come close to achieving the fewest number of encoder states possible. One of these codes has been implemented in a prototype system that supports M=6 discrete recording levels.