ExpressCard slot

The ExpressCard slot is a PC Card slot, that is not backwards compatible with the 32-bit CardBus or 16-bit PCMCIA standard.

There are 2 physical formfactors, ExpressCard/54 and ExpressCard/34. The numbers refer to the width of the ExpressCard in milimeters.
Electronically ExpressCards can be implemented as either PCI-Express or USB

ExpressCard/54 slots can accept ExpressCard/34 cards, but not the other way around.

• Wikipedia article on PCMCIA, PC Card, CardBus and ExpressCard

Linux support

ExpressCard adapters are handled either by the Linux PCI subsystem as hotplug PCI-Express adapters, or by the USB subsystem (depending on the adapter card).

Models featuring this Technology

ExpressCard/54

• R51e, R52
• T43, T43p, T60, T60p
• Z60m

ExpressCard/34 (using an adapter)

• X60, X60s