Electronic systems, such as automobile radios, portable and other computing devices, and global positioning system receivers, often require that a correct security code be inputted from a small memory card that is removably inserted into a card slot of the system before the system is rendered operable in total or in part, or before certain data can be retrieved. The same type of memory card is also used to store digital data that is utilized by the system in conjunction with its function that is enabled by the security code, such data cards being removably inserted into the same card slot as the card containing the security code. Alternately, both the utilization data and the security code are included on a single card. An example application is an automobile radio wherein data supplied by the second card are of music that is reproduced through the radio's audio system.