As the old saying goes, two heads are better than one. In the world of video game graphics, in most cases, two video cards are indeed faster than one. NVIDIA's Scalable Link Interface (SLI) proved to be quite popular despite the early growing pains of the GPU and chipsets. Long story short, it was up to game profiles, either built into the drivers, or put together by the user themselves to enable SLI for video games. For the most part, we don't have any major issues with NVIDIA's solution, and praised their Intel nForce 4 SLI upon release as being the best "gaming solution" available for Intel.

We've covered SLI plenty here at VL already, so I won't go much more into it specifically. During this time, ATI has been relatively quiet on the multi-graphics front. Hints and slips were common, but until actual hardware materialized, most of the hardware community took a wait and see approach for the day multi-graphics shows up from ATI.

That day is today as ATI officially unveils their Crossfire technology. What is Crossfire? Here's a snip from their press release:

When gamers add a CrossFire Edition graphics card, which includes the CrossFire compositing engine, to their Radeon Xpress powered system they are doubling their graphics rendering potential. With a variety of settings, they can use the rendering horsepower to get up to twice the performance of a single graphics card, or they can choose to put the horsepower to work increasing the image quality of their games, making them look better than ever before.

Much like NVIDIA, there are prerequisites as you can't run out and buy two X850XT cards and drop them into your existing motherboard. We'll compare and contrast ATI and NVIDIA's solutions shortly, but in the meantime, let's look into the Crossfire.

ATI X850 and X800 Crossfire Edition

What you can see above are engineering samples of Hightech Information System Limited's (HIS) X850 Crossfire card in conjunction with an ATI X850XT. Those of you with a boatload of PCI peripherals may want to clear out some motherboard and chassis real estate because depending on the configuration, you'll be losing up to 4 slots.

In a nutshell, the Crossfire cards don't differ all that much from the X8xx cards we've gotten used to. At least in the beginning, you can expect to see two variants of the hardware, the X850 Crossfire and X800 Crossfire. In essence, the VPU cores are identical to the non-Crossfire counterparts. The only real difference between them is the new Compositing Engine, which is a new chip built into the PCB (not the core itself).

By plugging in a special cable into the Crossfire's DMS slot, you run the other end into a spare DVI connection on your existing (or new if you don't already own an X8xx) card to have the setup running. The cable will be of the "Y" variety, so you will not lose functionality of the DVI connection.

Each card in the Crossfire array will have its own PCI Express link to the Northbridge. Each VPU and memory space can work on separate tasks, as well as sharing data. Once the VPUs are done processing the frame, it pushes the output to the Compositing Engine, which processes the information before outputting it to your computer display.

As you may expect, you can't match up a Crossfire edition with just any Radeon X8xx card. Here's a cheat sheet demonstrating the support.

X850 CrossFire Edition	RADEON X850 XT PE RADEON X850 XT RADEON X850 PRO
X800 CrossFire Edition	RADEON X800 XT PE RADEON X800 XT RADEON X800 XL RADEON X800 PRO RADEON X800 All-in-Wonder X800

As you can see, the Crossfire will work with older cards, such as the X800XT, though the caveat are the cards must be PCI Express based.

Xpress 200 CrossFire Edition Chipset

As mentioned earlier, not any old motherboard will work in a Crossfire setup. While you need to pickup a Crossfire Edition video card, as well as the matching non-Crossfire card, you will also need a motherboard based on the Radeon Xpress 200 CrossFire edition chipset. We don't have performance information regarding the chipset, though we do know that there will be support for both AMD and Intel (not on the same board naturally), as well as Dual Core support.

While only one nForce 4 SLI motherboard does it this way (that we're aware of), all the Xpress 200 CrossFire boards will handle the dual VPUs via the BIOS. This will make switching Crossfire on and off as simple as a reboot, without any fiddling with jumpers or PCB cards.

Final Words

The best way to understand the Crossfire is to think of a master and servant scenario (yes, THAT kind if you wish you pervs). You cannot go out and buy two X850s and plug in a connecting cable for this to work. The Crossfire Edition card runs the show, and the non-Crossfire is along for the ride, though it pulls its own weight.

You do not need to have two identical brands of cards (a HIS X850 Crossfire card will work with an ATI X850XT), though they must be the same class (refer to the chart earlier). Both cards need to have the same amount of memory, though the VPUs can be clocked different speeds. The nice thing about this is the master card will not throttle down its clock speed just to keep on level with the servant card.

If you decide to play chicken and the egg, and pick up a Crossfire prior to the secondary card, the card will indeed work in single mode. The X850 Crossfire falls within X850XT specifications and the X800 Crossfire the X800XL.

So, does ATI bring anything to the table that we have not seen already from NVIDIA? In some ways, they work the same; two matching series of cards, and a supporting motherboard. Unlike NVIDIA, gaming profiles aren't required for Crossfire. According to ATI, with the correct hardware, Crossfire is something that is enabled as soon as your PC is put together. Their approach is driver independent, so in theory, older games as well as newer games should work in Crossfire mode as soon as you fire them up. If this actually works as planned, this could be a major coup for ATI as it will make high-end gaming as close to plug and play as you get.