VIDEO THE PCI EXPRESS WAY
The jump from PCI to AGP (advanced graphics processor port) allowed PC graphics to get a performance boost, but at the expense of a specialized interface. Motherboards typically offered a single AGP slot, making multiple monitor support difficult until the advent of dual monitor adapters. The x16 PCI Express slot now provides the needed performance for high-end graphics, which makes PCI Express the way to go (unless the system has HyperTransport floating around).

Major video controller vendors ATI and Nvidia use PCI Express x16 as the platform for high-end graphics in lieu of the current AGP x8 standard. Nvidia possesses a range of PCI Express-based chips, starting with the GeForce PCX 5950 at the high end down to the entry-level GeForce PCX 4300.

IT'S IN THE CARDS
Migration to PCI Express means lots of hardware changes. Board sizes change. Connectors change. But the software stays the same.

PCI-SIG and PICMG bring a host of PCI Express adapter standards that handle x1, x4, x8, and x16 slots. The standards and sockets are designed so that a card with a lower number of lanes than the socket can still be plugged into the system. PCI Express autonegotiation will determine the card's capabilities and perform accordingly. Still, don't expect systems to have slots with the maximum number of lanes per slot. There's a cost associated with the PCI Express switch chips, so it pays to design a system to match its intended environment. An x1 slot supplies more than enough bandwidth for low-end peripheral and data-acquisition cards.

All card formats are getting a face lift. The PCI Mini Cards used in laptops have a corresponding PCI Express Mini Card standard from PCI-SIG (Fig. 2). It incorporates an x1 PCI Express connection, USB 2.0 link, and SMBus link. The latter is intended for management options. These cards can be used in embedded devices as well.

Likewise, the PCMCIA card and CardBus standards have a cousin in ExpressCard (Fig. 3). ExpressCard employs an x1 connection and pairs with a USB 2.0 and SMBus link. Sound familiar? ExpressCard comes in two form factors, both of which are smaller than a standard PCMCIA card.

PCI Mezzanine Cards (PMC) are getting a boost from the VITA-42 XMC standard for PCI Express. Cards using the standard can be employed on compatible VME and CompactPCI cards with XMC mezzanine slots.

PICMG's Advanced Mezzanine Card (AMC) standard will support a host of high-speed serial interfaces, including PCI Express, AS, and Ethernet. AMCs target AdvancedTCA carrier boards.

Additionally, the PCI-SIG is working on a Server I/O Module. This design compares favorably to the proprietary blade server solutions for enterprise-class servers. It's designed to deliver better hot-plug support plus improved power and cooling distribution. The boards fit into a compact cartridge.

Systems that take advantage of the PCI and PCI-X bus architecture like PC/104 will need to develop a new approach, because PCI Express doesn't lend itself to stacking. This is only a problem when using a separate motherboard. It will be interesting to see how or if PC/104 moves to PCI Express.

SO, WHEN?
PCI Express is here now. Servers, workstations, and laptops will lead the way this year in adoption, generating plenty of demand for PCI Express chips. This includes board-level products that utilize AdvancedTCA and CompactPCI form factors.

Expect PCI and PCI-X to travel on the same path as ISA. Both will remain fixtures on motherboards that will typically have x16 down to x1 PCI Express slots. The number of PCI and PXI-X slots will slowly drop to zero over the next 10 years.

Embedded designs will take a bit longer. PCI Express switch chips are readily available, but most developers would rather not contend with bridge chips. They would rather have CPUs and peripherals with PCI Express support. In the long run, this actually simplifies system designs, because it's simply a matter of choosing the appropriate processors, peripherals, and PCI Express switch chips.

On the horizon is the next generation of PCI Express. It will require new physical layers and may operate at 6.25 Gbits/s, more than twice the current standard. Backwards-compatibility will be mandatory for this standard. Look for standard ratification in 2005, though it will take a while for hardware to appear.

If you haven't looked at PCI Express yet, then it's recommended that you do so now. Don't wait for the next generation of PCI Express. Your competition isn't.

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