What is the ExpressCard Standard?

Don Bradbury overviews this increasingly popular expansion medium

The PCMCIA system expansion port has been around for many years, in recent times enhanced by the more advanced CardBus specification, and now followed by the ExpressCard standard.

Currently it's a toss-up, when you buy a notebook computer, whether you'll have CardBus fitted or the latest ExpressCard slot. The latter is winning the race because of its superior performance, and it can shortly be expected to replace CardBus as the expansion device of choice. Some notebooks have both fitted, in deference to the fact that so many will have accumulated a range of CardBus expansion cards over the years.

Each card type offers features especially suitable for use on a notebook - you can also get adapters to run them on a Desktop PC - but the ExpressCard standard delivers thinner, lighter, and faster expansion units in comparison with CardBus.

The Interface

All ExpressCard slots will accept modules that are designed to use either USB 2.0 or PCI Express standards. Speed is the main attraction of the latter, with bandwidth up to four times the speed of the old standard. This, in plain terms, means you can get faster music downloads with ExpressCards, smoother streaming video, and faster access to mass storage devices such as external drives.

ExpressCards come in broadly one of two variants - 54 or 34mm width - depending on several factors but partly down to the heat they generate and also the form factor required by the device. For example, CompactFlash and hard disk media would require the width of ExpressCard/54. But ExpressCard/34 and ExpressCard/54 are both accepted by the full size 54mm slot, so don't opt for a 34-only module if you're updating. In fact there are three variants altogether, the straight 54 and 34 options being the main designs, the graphic here showing all three types.

There is no direct performance difference between an ExpressCard/34 and an ExpressCard/54 module. Both variants use the same twenty six contact connector, so the computer doesn't care which type you use. If you add a 34 module to a 54 slot, there's a guide in the slot to push the device over to the left hand side where it slides into the required set of connectors.

The 54 form-factor allows for higher heat dissipation because of its larger surface area. Applications that run with substantial heat generation, such as high-speed data transfer modules, will generally be designed into an ExpressCard/54 module to take advantage of this.

The 34mm design is the favourite for manufacturers, however. It's smaller (of course), lighter, and less expensive to make. So as development of the standard is advanced, modules are expected to move towards the 34 standard where physically possible.

Technicalities

Technically, the ExpressCard interface may be summarised as shown in the following diagram, with the older PC Card also shown for comparison. ExpressCard is seen to be simpler, and it can make use of the near-universal USB 2.0 standard interface fitted to all modern PCs, as well as the PCI Express interface:

In terms of features, the chart below shows how the ExpressCard34 card is accommodated by the full width 54mm slot, as we explained, and also the older Cardbus connectivity which is via PCI/ISA. You might also be able to make out the crucial factor of the differing voltage which these two use, leading to the lower power consumption of ExpressCard which runs at 3.3 volts in comparison with CardBus running at 5.0 volts:

In Conclusion

As ExpressCards have faster interfaces, are lighter, and relatively cheaper to manufacture in comparison with the outgoing CardBus, they are being manufactured to cover every conceivable application, from USB and Firewire adapters to TV tuners, from media readers to docking stations, from mouse controllers to wireless LAN cards (WiFi), and from remote controllers to Bluetooth adapters. Essentially, you name it!

You can be certain that the list will expand as time progresses, simply because the form factor as well as the speed can accommodate so many differing end uses. It's a substantial step forward.

 

Don Bradbury