The unit includes a reader unit for reading out data from a data medium as analogue signals. A data conversion unit is provided for processing the data and an output unit for outputting the processed data. A start block detection unit (8) reads control data in the start block and stores it in a control data memory unit (9) as control data components. The data conversion unit (5) has data reconstruction elements (15,16,19-21.28) which can be supplied with associated control data components which are used to control the data processing. ADVANTAGE - Enables rapid, substantially error-free data processing, especially for high data density.