An unencoded m-bit data input sequence is divided into a block of n bits and a block of m-n bits. The block of n bits is divided into a first set of n+1 encoded bits, wherein at least one of P1 subblocks of the first set satisfies a G, M and I constraints. The first set of n+1 encoded bits is mapped into a second set of n+1 encoded bits wherein at least one of P2 subblocks of the second set gives rise to at least Q1 transitions after 1/(1+D.sup.2) precoding. A second set of n+1 encoded bits is divided into P3 encoded subblocks and the P3 encoded subblocks are interleaved among (m-n)/s unencoded symbols so as to form a (m+1)-bit output sequence codeword which is then stored on a data storage medium.