ATI CrossFire - Hands on

For a detailed overview of the technologies involved in CrossFire, see Tim's CrossFire preview article.

For those of you just tuning in or wanting a refresher, here's a quick run through of what CrossFire offers...

Extra performance in every game, not just profiles

CrossFire supports three different types of rendering - Alternate Frame Rendering and Split Frame Rendering, just like SLI, but also Super-tiling. Profiles can be used on CrossFire to specify one method over the other, and ATI implement these in their drivers, it appears. However, where there is no profile, the hardware will drop back to Super-tiling, which is designed to be compatible with all types of games. Super-tiling splits each frame up into tiles, like a chess board, and then uses one card to render one set of titles and the other card to render the other set.

This universal compatibility, seamlessly, is something that NVIDIA still does not offer, despite crude attempts to allow for registry hacks to do so and as such, is a major selling point of CrossFire.

Does it work?
Well, the answer is 'We can't get it to at the moment'. We tried CrossFire with two, as-yet-unreleased titles - Half-Life 2: Lost Coast, and Serious Sam 2. Neither of them worked under NVIDIA SLI, because NVIDIA haven't released a profile for these titles (although we fully expect them to be supported when they hit the shelves). However, with the universal performance gains touted by ATI, we were hoping that Super-tiling on CrossFire would result in an increase in performance right now.

We got no performance gain with Lost Coast when running at 1024x768, 2x/8x over running a single X850 card. We were able to stick on CrossFire AA, but it totally killed the framerate and the game became unplayable. In Serious Sam 2 (tested using FRAPS), we saw around a 4fps increase with CrossFire enabled, which is well within the margin of error for a single card. Analysing the framerate log in FRAPS showed that CrossFire wasn't making a difference to our performance.

We've asked ATI to find out why CrossFire isn't acclerating these games. We turned off Vsync in the driver, and there's nothing that should prevent us seeing Super-tiling in action in these games. We'll update this preview as soon as we've got a response back from the technical guys at ATI. However, right now, it looks as though Super-tiling in every game out there doesn't work.

SuperAA

There comes a point at which more frames per second becomes pointless, and you'd rather improve image quality. This is what CrossFire Super Anti-Aliasing is for. By combining the power of the cards, you can have up to 14xAA on an image, making for outrageously good image quality.

Does it work?
Yes. At 1280x1024 with 14xAA, you can fire up Far Cry, Half LIfe 2, or any current game and absolutely keel over at the image quality. It simply looks gorgeous - below is a screen capture of Lost Coast at 1024x768 with 14xAA. (Click to enlarge)