ExpressCard
ExpressCard is a hardware standard replacing CardBus PC cards, both developed by the Personal Computer Memory Card International Assocation.

Form Factor
ExpressCard supports ExpressCard/34 (34mm wide). The 34 mm form factor cards fit into both 34mm and 54mm card slots.

Comparison to CardBus
The major benefit of ExpressCard technology over the previous PCMCIA CardBus PC Card is a dramatic increase in bandwidth, afforded by the fact that the ExpressCard has a direct connection to the system bus over a PCI Express x1 lane or USB 2.0, whereas CardBus utilizes an interface controller that only interfaces with PCI. The ExpressCard has a maximum throughput of 2.5 Gbit/s through PCI Express or 480 Mbit/s through USB 2.0 dedicated for each slot, versus CardBus's shared 1066 Mbit/s bandwidth.

In addition, the ExpressCard standard uses lower voltages and thus less power than the previous CardBus slots (1.5V and 3.3V versus 3.3V and 5.0V).

The ExpressCard interface is not backwards-compatible with CardBus devices.