When the PowerBook Duo computer is housed in the Duo Dock, you cannot access the integral modem via the RJ-11 connector on the PowerBook Duo's rear panel. A modem adapter card provides the connection. It plugs into the side of the Duo Dock's main logic board, using a 10-pin header connector. The card supplies the RJ-11 hook up, which is accessed on the rear panel of the Duo Dock. The adapter card interfaces with the modem card in the PowerBook Duo computer via its 10-pin connector, printed circuit traces, and the 152-pin expansion connector.