Digital servo control system for use in disk drives

In an information storage device having a recording medium and a reading device for reading information from the recording medium, an arrangement for controlling the reading device's position relative to the recording medium by processing position samples encountered in respective sample periods and for providing an effort signal before a subsequent sample period to control the position of the reading device relative to the recording medium, the arrangement comprising:

• a) at least one position information area embedded between information in the recording medium, the position information area including a fractional positional information area that the reading device encounters only once per sample period and that includes at least one dibit pair allowing determination of the reading device's position with a precision substantially smaller than a width of information tracks in the recording medium;
• and
• b) a position control device, responsive to only one dibit measurement per sample period from only one dibit pair per sample period from the reading device, the position control device including:
• b1) means for pre-processing the dibit measurement to compensate for non-ideal characteristics of the dibit measurement, and for generating a pre-processed signal for each dibit measurement;
• and
• b2) means, responsive to the pre-processed signal, for generating the effort signal.