Inspecting the Hardware
For CrossFire to function properly, you need three things -- a CrossFire Edition Radeon graphics card, a standard Radeon card of the same family, and a CrossFire ready motherboard with two PEG slots. By now you've all seen what a standard Radeon X850 XT looks like, but you may not have laid eyes on a CrossFire Edition Radeon X850 XT "master" card and a properly configured Radeon Xpress 200 CF Edition motherboard, so take a look.
On the surface, the CrossFire Edition Radeon X850 XT looks very much like a standard Radeon X850 XT. The general layout of the PCB is the same; they use the same two-slot GPU cooler, and the cards are the same height and width. There are obviously some major differences though. First off, if you view the front of the card, you'll notice the proprietary CrossFire DMS-59 connector. The DVI output from the standard Radeon is fed into the DMS-59 connector through the use of a custom dongle, and on the end of the dongle is another DVI connector which feeds the primary display.
Another minor difference we found the differentiates a CrossFire Edition card from a standard Radeon is a small 14-pin header on the backside of the PCB. Representatives from ATI say this header will likely not appear on retail versions of the card, and that it is used for internal testing only. We asked if this was some sort of internal connector that will eliminate the need to use a dongle to link two cards, but were told ATI had no plans to do this just yet. They weren't very convincing in their explanation of this header, however, so we thought we'd point it out anyway.
ATi Radeon CrossFire Edition
The most dramatic different between a CrossFire Edition Radeon and a standard card lies beneath its heatsink. Underneath the heatsink, towards the front of the card near the DVI connector, is the CrossFire Edition's compositing engine. The compositing engine is what makes CrossFire possible. This main device in the engine is a Xilink Spartan 3 FPGA (Field Programmable Gate Array), and it is flanked by an Sil 1161, a TI TFP401 PanelBus Digital Receiver chip and an EPROM. We're going to hazard a guess that this three chip set, along with the Xilinx configuration EPROM costs somewhere in the neighborhood of $20 - $25. This is added cost overhead to the overall solution for sure, but it also adds significant flexibility in the future as the progammable nature of the solution allows for the possibility of updates back at the factory and possibly even at the end user firmware level.
The compositing engine is what's responsible for assembling the final image from each GPU before it is sent to the display. The compositing engine will only be used on CrossFire Edition "master" cards; the companion Radeon card used to complete the CrossFire requirement doesn't have to be a CrossFire based version. There is a major limitation with this version of ATI's compositing engine, in that its causes an X800 series CrossFire Edition cards to display video at a maximum resolution / refresh rate of 1600x1200x60Hz for CRT's and 1920x1200x52 Hz for LCD's when in CrossFire Mode (2D is not affected). This was a conscious decision made on ATI's part to keep costs down, and to maintain compatibility with the limited bandwidth offered on the single-link DVI outputs on existing Radeon cards.
The Radeon Xpress 200 CrossFire Edition motherboard we received for evaluation was an ATI reference design, based on a black PCB with red accents. It is unlikely that this exact board will hit retail shelves, so we won't spend too much time discussing its virtues. This board is essentially very similar to the reference Radeon Xpress 200 motherboard we looked at in November, but this version has its 16 PCI Express lanes reconfigured in an 8x8 configuration to support a pair of graphics cards, and it's got built-in support for Hi-Def audio. The board was fairly well laid out, and had heatsinks in the VRM and on the North and South bridge chips. The Northbridge actually had an active cooler, but ATI claims that passive cooling would work fine as well.