Abstract: A data storage system has a rotatable magnetic disc with a plurality of concentric tracks. The system also has read/write circuitry for writing data to the tracks and reading data from the tracks at various frequencies and for pre-compensating the data written to the tracks to compensate for intersymbol interference. Frequency zones are established for the tracks by preliminarily assigning each track to one of a plurality of frequency zones. The pre-compensation is adjusted based on the intersymbol interference which occurs using the preliminary assignment of the tracks to the frequency zones. Data is then written to the tracks and the window margins for the data are tested to see if they meet a threshold window margin. If the window margins do not meet the threshold window margin, the assignment of the tracks to the frequency zones is adjusted and the pre-compensation is also adjusted.

Abstract: A phase lock loop includes a phase shift apparatus to provide a plurality (i.e., four) phase-shifted clock signals from the VCO. A phase selector is responsive to a triggering signal from a one-shot multivibrator to select the one phase-shifted clock signal next following termination of the trigger signal. The one-shot is responsive to a change between the read and write mode to initiate operation of the phase selector. As a result, the initial phase error between the input signal (read pulses or write clock) and the clock signal of the phase lock loop is no more than 1/8 window.