The functionality provided to electronic devices by application specific removable modules is enhanced by viewing the removable modules as first-level removable modules and providing them with at least one second-level removable slot for selectively nesting second-level removable modules having particular external I/O capabilities. The functionality provided to the electronic devices by such a first-level removable module can thus be provided in part by the application specific circuitry within the removable module and further in part by the type of external I/O of the second-level removable module.