Abstract: A data processing device for variable length formats includes a control unit and a storage unit coupled to the control unit. Two data exchange buses are each coupled to a respective data input and to a respective data output of the storage unit. Two switches are coupled to the control unit and to respective data exchange buses. An arithmetic/logic unit is coupled to the control unit, to the switches and to the storage unit. A data shaft unit is coupled to the data exchange buses and to the control unit. A data masking unit is coupled to the data exchange buses, to the control unit and to the switches. This device enables the preparation for processing of multibyte data fields arbitrarily arranged with respect to the word boundaries in main storage. The data shift unit provides automatic alignment of the bytes of the operands relative to each other. The data masking unit masks irrelevant bytes of the first and last words of each operand.