Caught In The CrossFire

ATI's SLi beating twin graphics card solution is unveiled, but how will it compare to nVidia's already established platform.

ATI’s answer to SLi is here and the official name is – wait for it – CrossFire. Alright, this has already made its way out on the web as it’s hard to keep secrets in the computer world. So ATI has come up with a catchy name, but a name is not enough to make a product great. ATI has kept very quiet about what CrossFire can do and how it will work, so on Thursday last week it gathered a bunch of European journalists and several of its UK partners in London to show us what all the fuss was about.


The presentation started with a brief about the Xbox 360 and the ATI technology fitted inside it, which looks pretty cool on paper at least. The Xbox 360 has native support for HDTV and – while this is only at 720p – every game will run with 4x FSAA enabled without any performance degradation – very nice.

Anyway onto the matter at hand, which is far more interesting if you own a PC. ATI had brought along a demo system and everyone was made to look inside to try to figure out what we were going to be shown. As expected, we saw two graphics cards but surprisingly they looked slightly different from one other and you’ll soon understand why.


You see, with nVidia’s SLI solution you can use any two cards of the same type from the same manufacturer (although there may still be issues with BIOS revisions). By contrast, CrossFire can use ATI cards from different manufacturers, as long as one of them is a “CrossFire Edition” card. Yes, you read that correctly: the CrossFire Edition card will be different to the standard X8xx card that you may already own. Once you have this CrossFire Edition card though, it will work in conjunction with any existing PCI Express X800 or X850 card. Technically, CrossFire could be made to work with other ATI PCI Express cards, such as the X700 series, but stated that it was focussed only on the X800 and X850 ranges at the moment.

Onto the mechanics: the two cards are connected via an external DVI pass-through cable and here is where it gets interesting (so pay attention!). The CrossFire Edition card has what ATI calls a compositing engine which blends the output of the two cards together. As far as I could tell from the card on display at the presentation, this compositing engine is made by Silicon Image and not ATI. What is clever is that there shouldn’t be any image quality degradation as it’s a digital signal that is being passed on from one card to the other. So anyone who remembers the soft images that resulted from Voodoo and Voodoo 2 cards can relax, you won’t be squinting at your desktop with a CrossFire setup.


Now, there are four different ways that CrossFire works: AFR (Alternate Frame Rendering), Scissor mode (split screen rendering), SuperTiling (each card is given an equal part of an area to render and the two are then put together by the compositing engine) which according to ATI will offer the best performance and finally Super AA mode. The Super AA mode doesn’t add any performance advantage over a single card, but can utilise up to 14x FSAA (14x!). According to ATI, this allows for far greater image quality, especially when it comes to “micro-geometry”, meaning that you don’t lose out on very fine details.

More impressively, ATI claims that CrossFire will boost the performance of every game on the market and there will be no need for specific profiles or downloads to enable it. If this is true, ATI really has a winner on its hands.

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