This disclosure concerns for generating asymmetrically constrained run-length-limited encoded data from a serialized binary string of 1's and 0's. The method comprises the steps of encoding the input data bits using a run-length-limited constraint in the form of M/N (d,k), where M is the number of input data bits, N is the number of output bits associated therewith, d is the minimum number of 0 data bits between adjacent data bit 1's, and k is the maximum number of 0 data bits between adjacent 1's; and alternating the values of d and k between a set (d.sub.1, k.sub.1) and a set (d.sub.2, k.sub.2), respectively, where d.sub.1 .noteq.d.sub.2. The apparatus comprises means for generating N output data bits in response to M input data bits and for generating data bit 0's between data bit 1's based upon a run-length-limited coding constraints (d.sub.1, k.sub.1) and (d.sub.2, k.sub.2), where constraints (d.sub.1, k.sub.1) and (d.sub.2, k.sub.2) apply alternately to runs of zeroes between output data ones. Fractional numerical values of d.sub.1 and d.sub.2 can be employed in the method or apparatus.