A reading unit for reading data from a digital data carrier, the reading unit comprising: a reading head including a sensor for sensing data from the data carrier and generating a sensor signal indicative for the sensed data; head positioning apparatus for positioning the head relative to the data carrier in response to a head positioning control signal; a head positioning controller for receiving the sensed data and being operable in accordance with a stored instruction set to process the sensed data to generate the head positioning control signal; and a data decoder for decoding the sensed data to form a digital output signal.