Controller for a printing unit comprising a standard hardware board (B) provided with a central processing unit (10), an I/O-unit (12) and a central bus system (14) connected to the central processing unit and the I/O-unit, the I/O-unit comprising a connector (16) for connecting the central bus system to a memory board (22) that comprises one or more memory chips (24) for storing bitmap data or compressed bitmap data of a page to be printed,wherein the memory board (22) has a second bus system (36) and a memory reader (26) connected to the memory chips (24) via the second bus system (36) for reading the data and transmitting them to a printer (28).