The tide is turning for PCI Express (PCIe), but certain currents are running faster than others. The PC side is a veritable flood as vendors push the edge, especially when it comes to graphics (see "Bevy Of Computer Parts Adds Up To A Banner Year" at www.electronicdesign.com, ED Online 11573) and RAID storage (see "Building A SAS RAID File Server" at ED Online 12386).
Internally, laptops have made the same move. But plug-in interfaces using ExpressCard are just showing up now. Embedded is even slower, though there are standards like COM Express (see "COM Express: A New Standard" at ED Online 8780), AdvancedTCA, and a horde from VITA (see "Bus and Board Show: Part 1" at ED Online 11977).
The availability of components, the European Union's Restrictions on Hazardous Substances (RoHS), and general confusion hold PCI Express back on the embedded side. Luckily, PCI Express support chips, hosts, and peripheral chips are becoming more available. Also, RoHS is a shortterm issue. It seems that the distraction to redesign existing products to meet RoHS standards has put new designs on the back burner. This should change by the end of the year too.
Now there's general confusion. It's somewhat a problem of our own making, though. Standards like ExpressCard employ two standards, USB and PCI Express. But an ExpressCard typically will use only one. For example, Novatel's line of wireless adapters uses USB (Fig. 1). Yet SIIG's 3-Gbit/s SATA-II card uses PCI Express because of its higher bandwidth requirements (Fig. 2).
Standards such as COM Express and EPIC Express incorporate PCI Express and parallel buses for backward compatibility. At this point, EPIC Express is gaining ground, with variations of the standards reducing the dependency on PCI Express. The new standards eventually will dominate, but it appears that this will occur a few years later than many of us expected.