The media/data card is a computer readable medium for storing data files, and in particular, media files. The device may be a flash media memory card or other conveniently sized, portable storage device. The media/data card stores a data structure for controlling access to data files stored on the computer readable medium. The data structure includes a media storage substructure for storing the data files, a file system directory substructure containing the locations of the data files stored in the media storage substructure; and a security substructure for describing allowed access to the data files stored in the media storage substructure. The data files may be multimedia files, such as compressed audio or video files. The data files may be encrypted to provide enhanced security.