Personal Computer Memory Card International Association (PCMCIA) is the consortium of computer manufacturers that devised the standards for the credit-card style adapter cards used in many notebook computers.
PCMCIA defines three types of cards:
TYPE I: Cards that can be up to 3.3 mm thick, and are generally used for RAM and ROM expansion cards.
TYPE II: Cards that can be as thick as 5.5 mm, and typically house modems or fax modems.
TYPE III: Cards that can be as thick as 10.5 mm, and are mostly used for hard disks.