PC Cards come in three types. All PC Cards have the same width and length - 54.0 millimeters wide and 85.6 millmeters long - but vary in thickness:
Type 1 - 3.3 millimeters thick
Type 2 - 5.0 millimeters thick
Type 3 - 10.5 millimeters thick
Ethernet PCMCIA network adapters were originally all Type 2 PC Cards. These cards feature a dual-speed or Fast Ethernet jack and sometimes a second jack for an onboard dial-up modem. Type 1 PC Cards cards generally contain computer memory and Type 3 cards generally contain disk storage.
Type 2 PC Cards are too thin to fit a full-sized Ethernet (RJ-45) jack and/or a full-sized phone (RJ-11) jack. Instead, Type 2 Ethernet PCMCIA cards require proprietary jacks and short external cables called dongles that interface a proprietary jack to a standard one.
However, an increasing number of PCMCIA Ethernet adapters are now being built using the Type 3 form factor. Being twice as thick as Type 2 adapters, Type 3 adapters work without dongles because they fit a full-sized Ethernet (RJ-45) jack and/or a full-sized phone (RJ-11) jack. One Type 3 ("double high") adapter fills both PCMCIA slots in a notebook computer.