Abstract: A maximum likelihood detector for a disc drive in which data files are stored along tracks as a sequence of magnetically written data elements that give rise to a signal in the disc drive read chapel. The detector includes even and odd Viterbi decoders that determine the most likely even and odd subsequences of data elements from even and odd samples of the signal and a postcoder that generates the most likely sequence of bits of encoded user data from the subsequences.

Abstract: A method for assigning tracks on a magnetic data storage disk to different zones in which data is written at selected zone frequencies so as to write data on the tracks at the maximum frequency that will limit the read/write error rate to a preselected value. A plurality of data bit groups is written onto selected tracks and read while checking for error to determine an error indication parameter for each of the zone frequencies. Tracks are assigned to frequency zones by determining such parameter for all tracks and assigning each track to the zone corresponding to the maximum frequency for which the error indication parameter is below the preselected value or by determining circular paths at which the error indication parameter has the preselected value for each of the selected frequencies and assigning all tracks between two consecutive circular paths to the lower of the two frequencies defining the circular paths.