Abstract: A personal digital assistant module with a local CPU, memory, and I/O interface has a host interface comprising a bus connected to the local CPU and a connector at a surface of the personal digital assistant for interfacing to a bus connector of a host general-purpose computer, providing direct bus communication between the personal digital assistant and the host general-purpose computer. In an embodiment, the personal digital assistant also has a means for storing a security code. The personal digital assistant according to the invention forms a host/satellite combination with a host computer having a docking bay, wherein upon docking a docking protocol 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.