XJACK is a type of connector for notebook computer modem that allows a standard telephone connector to snap into the modem. Internal modems for notebook computers come on a slim Personal Computer Memory Card International Association ( PCMCIA ) card. Many cards provide a connection that requires a special plug that in turn has to be plugged into a relay attachment. This plug can easily become loose in the PCMCIA socket, losing your connection. XJACK is a connector on the PCMCIA card that pulls out and allows you to snap a regular wall jack connector into the modem directly. This connection is more secure.
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XJACK was originally manufactured by Megahertz, a subsidiary of U.S. Robotics. However, a number of other modem manufacturers now build the XJACK into their mobile-size modems.