A miniature digital assistant module with a local CPU, a memory, and a touchscreen I/O interface in a preferred embodiment, has a host interface comprising a full-service parallel bus, including data lines, address lines, read/write signals, and at least one memory control signal, connected to the local CPU and also to a connector at a surface of the personal digital assistant. The full-service bus connection provides direct bus communication between the personal digital assistant and a host computer. In a preferred embodiment, the miniature digital assistant also stores a security code, which the host can recognize. The miniature digital assistant forms a host/satellite combination with the host computer, which has a docking bay. When the miniature digital assistant is docked, a docking control routine controls access by the host to memory of the personal digital assistant based on one or more passwords provided by a user to the host. In an alternative embodiment the personal digital assistant also has an expansion port connected to the local CPU, and expansion peripheral devices may be connected and operated through the expansion port, even while the miniature digital assistant is docked.