PC Card 
A type of credit-card-size device that plugs into a notebook computer to add functionality, such as in a modem or a network adapter, or additional storage capacity. These devices conform to standards set by the Personal Computer Memory Card International Association (PCMCIA): Type I PC Cards are 3.3mm thick and used mainly to add memory; Type II cards are 5mm thick and often are used for modems and LAN adapters; Type III cards are 10.5mm thick and are often used for hard drives.