For storage of data on data carriers accommodated in cassettes (28), a device is used with a magazine, having receptacles for cassettes (28) and with a robot unit (44) for changing the cassettes (28) between the receptacles and a drive (16). The magazine is movable relative to robot unit (44), in order to position the selected receptacle for changing of the cassette (28). For positioning, a sensor unit is provided on robot unit (44) and a light guide element on each receptacle. The light emitted from the light transmitters of the sensor unit is guided via the light guide element to the light receivers of the sensor unit, when they are congruent with the positioning position of the robot unit (44) and receptacle.