Abstract: The apparatus permits non-disruptive addition and removal of PCMCIA modules from a host device. The host device includes a signal bus connected to mating pins of the card header. The card header has a three-sided frame into which a module is inserted. A switch disposed on an edge of the header is responsive to insertion and de-insertion of the module. The length of the mating pins vary where selected mating pins of the card header have a first length for detecting substantially complete insertion and partial de-insertion of the module, and pins of a second length for applying bus signals to the module. Pins of a third length facilitate applying electrical power to the module. The computer is responsive to the switch and the mating pins such that the signal bus is deactivated to prevent corruption of the bus signals when the switch detects insertion of the module. The signal bus remains deactivated until the module is in communication with pins of a first length, whereupon the signal bus is then reactivated.