PC Cards (PCMCIA)

In an effort to give laptop and notebook computers the kind of expandability that users have grown used to in desktop systems, the Personal Computer Memory Card International Association (PCMCIA) has established several standards for credit card-size expansion boards that fit into a small slot on laptops and notebooks. The development of the PC Card interface is one of the few successful feats of hardware standardization in a market full of proprietary designs.

The PC Card standards, which were developed by a consortium of more than 300 manufacturers (including IBM, Toshiba, and Apple), have been touted as being a revolutionary advancement in mobile computing. PC Card laptop and notebook slots enable you to add memory expansion cards, fax/modems, SCSI adapters, network interface adapters, and many other types of devices. If your computer has PC Card slots that conform to the standard developed by the PCMCIA, you can insert any type of PC Card (built to the same standard) into your machine and expect it to be recognized and usable.

The promise of PC Card technology is enormous. There are not only memory expansion cards, tiny hard drives, and wireless modems, but also ISDN adapters, MPEG decoders, network interface adapters, sound cards, CD-ROM controllers, and even GPS systems that use global positioning satellites to locate your exact position on the earth.

Originally designed as a standard interface for memory cards, the PCMCIA document defines both the PC Card hardware and the software support architecture used to run it. The PC Cards defined in version 1 of the standard, called Type I, are credit card size (3.4x2.1 inches) and 3.3mm thick. The standard has since been revised to support cards with many other functions. The third version, called PC Card Specification -- February 1995, defines three types of cards; the only difference between each one is their thickness. This was done to support the hardware for different card functions.

Most of the PC Cards on the market today, such as modems and network interface adapters, are 5mm thick Type II devices. Type III cards are 10.5mm thick and are typically used for PC Card hard drives. All of the card types are backwards compatible; you can insert a Type I card into a Type II or Type III slot. The standard PC Card slot configuration for portable computers is two Type II slots, with one on top of the other. This way, a single Type III card can be inserted, taking up both slots but using only one of the connectors.

For more information on the PCMCIA standard, check out http://www.pc-card.com.