Abstract: Portable computing hosts, such as PDAs, are customized for use in diverse applications, such as media and game players, through use of a first-level removable expansion module having player-specific circuitry and a slot for a second-level removable module, such as a removable memory. For example, in combination with a connected or attached user interface device (e.g., earphones), these modules provide a host with external-interface circuitry and/or application-specific functions as well as second-level removable memory functions. The removable memory may be used to store and playback digitally encoded media such as music, audio, or video. The removable memory may also be used directly or predominantly by the player's application specific circuitry within the first-level removable expansion module.