Techniques for implementing non-uniform constraints in modulation encoded data

A disk drive controller chipset comprising:

• a modulation encoder that imposes a first constraint on a codeword starting at a first bit location and that imposes a second constraint on the codeword starting at a second bit location to generate an output codeword, wherein the second constraint is more strict than the first constraint;
• and
• a multiplexer that inserts a block of unconstrained data into a portion of the output codeword that is constrained according to the second constraint before the output codeword is stored on a disk.

A method for imposing modulation constraints on data, the method comprising:

• imposing non-uniform modulation constraints on a codeword to generate a constrained codeword;
• and
• inserting unconstrained data into a more strongly constrained portion of the constrained codeword before the constrained codeword is stored on a medium.