Support Report
PCI-Express and the UAD-1
by Jor van Gelder

PCI Express (PCIe) is an exciting new I/O interconnect bus standard gaining wide acceptance in the computer market. It will replace the PCI, PCI-X, and AGP parallel buses over the next few years (and most likely FireWire, as well), much like PCI replaced ISA several years ago. The benefits of PCIe are clear for the industry and the end-user. PCIe is a high-speed serial point-to-point protocol that offers far greater bandwidth, lower cost, increased flexibility, better scalability and increased efficiency over existing parallel multidrop buses like PCI, PCI-X and AGP.

(Note: Don't confuse PCI Express with PCI-X! PCI-X is an enhanced version of PCI, and is backward-compatible with existing PCI cards. PCI Express is not backward-compatible, because it uses a completely new connector and electrical interface.)

The PCI bus has served us well for the past ten years, and it will play a major role in the next few years. However, processors and I/O devices are now demanding increasingly greater I/O bandwidth than PCI or PCI-X can deliver, and it is time for a new generation of PCI to serve as a standard I/O bus for future-generation platforms.

“The PCI bus has served us well for the past ten years, and it will play a major role in the next few years. However, processors and I/O devices are now demanding increasingly greater I/O bandwidth than PCI or PCI-X can deliver, and it is time for a new generation of PCI to serve as a standard I/O bus for future-generation platforms.”

As with many major PC architecture changes, the transition from PCI to PCI Express won't happen overnight. PCI Express is not intended to replace PCI or PCI-X immediately. Rather, the PCI Special Interest Group (PCI-SIG) will continue to support both standards, because both have attributes that are needed on a per-application basis. As proof of this, consider the fact that PCI/PCI-X and PCI Express slots will coexist in the same machines in the future and be used for different types of interconnects. (PCI Express is, however, intended to replace AGP.) Expect to see at least one or two standard PCI slots along side PCIe in all motherboards for at least the next few years. Just as ISA slots stuck around for nearly ten years before they were finally gone, your PCI peripherals, including the UAD-1, will likewise continue to be supported by new motherboards for many years.

Here is what this new technology means for UAD-1 users:
PCI-Express is completely software-compatible with PCI-compliant hardware. This means the PCI drivers shouldn't need to be changed to support PCIe. Intel has already stated that all current operating systems will support PCI-compatible interface cards in the new PCI-Express system, using existing PCI drivers.

This means that you can safely install a UAD-1 and the UAD-1 software in a system that integrates PCIe alongside PCI (and possibly in PCIe slots using a PCIe-to-PCI bridge like those offered by SBS Technologies). However, PCI-Express is not physically backward-compatible with PCI/PCI-X devices. (A PCI card will not fit into a PCIe slot.) So, if you plan to purchase a motherboard with PCIe, make sure that the board also offers the number of PCI slots you will need for your UAD-1 cards and any other PCI cards you still wish to use.

Almost all systems emerging on the market are designed with this change in mind and will feature both PCIe and PCI or PCI-X slots. The UAD-1 has been successfully installed in a variety of such systems, and there are no known compatibility issues with any new motherboards or chipsets featuring PCIe.

Table: Peak Bandwidth by Bus Protocol