Runlength-limited code and method

A method of runlength-limited coding blocks of N+B bits (N and B positive integers), comprising the steps of:

• (a) runlength-limited coding N bits to form a codeword of N+j bits where N and j are positive integers, said codeword characterized by (i) the first m bits (m a positive integer) decode into only the first K bits of said N bits and (ii) the last n bits (n a positive integer) decode into only the last K bits of said N bits;
• and
• (b) forming a second codeword of N+B+j bits (B a positive integer) by taking the first m bits to be the same as the first m bits of said N+j bit codeword, the next b bits (b a positive integer less than B) to be independent of said N+j codeword, the next N+j−m−n bits to be the same as bits m+1 through N+j−m of said N+j codeword, the next B−b bits to be independent of said N+j codeword, and the last n bits to be the same as the last n bits of said N+j codeword.