PC Card

A credit-card sized, removable module for portable computers standardized by PCMCIA. Also known as "PCMCIA cards," PC Cards containing a modem, network adapter, sound card, radio transceiver, solid state disk or hard disk can be plugged in while the computer is turned on ("hot swapped"). Early laptops were more limited than their desktop counterparts, and PC Cards provided a mechanism for internal expansion. For more information, visit www.pcmcia.org.

PC Card Types (Introduced 1990)
PC Cards use a 68-pin connector and have an 86x54 mm (3.4x2.1") form factor. Laptop computers often have one or two Type II slots; however, newer laptops may only support ExpressCards (see below).

    Type    Thick x Long x Wide (Millimeters)

      I     3.3 x 86 x 54 mm
     II     5.0 x 86 x 54 mm
    III    10.5 x 86 x 54 mm

CardBus (Second Generation - 1995)
Same size modules as PC Cards, CardBus cards are based on the 32-bit PCI bus, and data transfer speed was increased to a maximum of 132 Mbytes/sec from 40 Mbytes/sec for 16-bit PC Cards. CardBus also accommodates cards of different voltages and supports bus mastering and power management.

ExpressCard (Third Generation - 2003)
ExpressCards are smaller than PC Card/CardBus modules and come in two sizes: 5x75x54 mm and 5x75x34 mm. Designed for desktop and mobile use, ExpressCards use either USB 2.0, single lane PCI Express or both interfaces at the same time, providing up to 342 Mbytes/sec in one direction. See ExpressCard, PCI Express and USB.

Card and Socket Services
Card Services and Socket Services are the drivers for PC Cards. Card Services manage hot swapping and automatically configure the system resources required by the card (IRQs, memory and I/O addresses on a PC). Card Services talk to Socket Services, which is low-level software that talks directly to the PC Card controller chip. Socket Services are built into the system BIOS.

PC Card/CardBus and ExpressCards

PC Card and CardBus form factors are the same (left). The ExpressCards (middle and right) changed the format. (Image courtesy of Personal Computer Memory Card International Association, www.pcmcia.org)

The PC Card

The PC Card (left) on laptops is the equivalent expansion mechanism to the printed circuit board (right) on desktop computers.

Desktop Readers

PC Card drives can be added to desktop machines, either externally (top two) or internally (bottom). The unit in the middle is actually a SCSI hard drive with a built-in slot. (Image courtesy of Microtech International, Inc.)

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PC Card - Personal Computer Memory Card International Association