PC Cards are self-contained extension cards especially for laptops
and other types of portable computers. In just about the size of a
credit card they provide functions like LAN cards (including
wireless LAN), modems, ISDN cards, or hard disk drives - often
"solid-state" disks based on flash chips.
The PC Card technology has been has been developed and standardized by the
Personal Computer Memory Card International Association (
PCMCIA),
see
http://www.pcmcia.org/pccard.htm .