ATI Radeon X850 XT CrossFire Review

ATI fights back against NVIDIA with their dual card solution known as CrossFire. Although CrossFire improves performance, do the limitations that exist in ATI’s current dual card implementation make CrossFire a wise investment?

Grammatical & Spelling Editor: Timothy Daniel


It has been almost a four full months since ATI launched their ATI CrossFire technology. We wrote a preview of this technology way back on May 30 of 2005. This initial technology preview was very clearly a paper launch. Since that time, gamers and reviewers have been waiting with baited breath for a chance to get to use a CrossFire setup. That time has finally come nearly four months after we first heard about it. I believe it is important and fair to note that initially NVIDIAآ’s dual card solution, Scalable Link Interface (SLI), was also paper-launched. NVIDIA released information regarding SLI and we wrote a tech preview on it on June 27th of 2004, but we actually did not have hardware in hand until nearly five months later in November of 2004. NVIDIA clearly has the lead on ATI with their dual card solution having been out close to a year now while ATIآ’s dual card solution is just now coming to market. In that yearآ’s time, ATI has not released their next generation video card lineup, while NVIDIA has.

To recap what CrossFire is all about, the idea is quite simple; take two video cards and connect them together in such a way that they can provide a performance boost for you in games. With this extra performance, you have the ability to raise the resolution, enable anti-aliasing (AA) and anisotropic filtering (AF), and turn on the highest level of in-game quality settings, or at least get closer to those goals. NVIDIAآ’s technology aims to do the same thing, but they call their technology SLI. Now it is ATIآ’s turn to show us what their dual video card solution can do.

Just as NVIDIAآ’s SLI encompasses an entire ecosystem of components, ATIآ’s CrossFire platform does so as well. Right now, the requirement is that you have a motherboard based on the Radeon Xpress 200 CrossFire edition chipset. This is much like SLI, which requires an nForce4 motherboard chipset. However, as most enthusiasts know, the nForce4 is a very fast, stable and feature rich chipset for gamers right now. With our testing of the provided ATI Xpress 200 motherboard, we experienced the same level of stability and performance as the nForce4. There is also a possibility that future Intel chipsets may support CrossFire out of the box.

The next component to making CrossFire work is the CrossFire master card. Unlike SLI, you cannot take two identical video cards and connect them for dual video card operation. With ATIآ’s implementation, you must purchase a separate CrossFire master card that works for either the X800 or X850 series of video cards. This master card contains a special compositing engine chipset and DVI connector on it to enable dual video card support. Obviously, the last requirement is that you have an X800 or X850 series video card already so that you can use it in tandem with the CrossFire master card. Please read our tech preview to learn more about how this all works.

Once you have all of the required components, setting up CrossFire is as simple as enabling it the driver control panel. Weآ’ll go into more detail regarding installation on the next page. In order for the driver to work, you must have Catalyst A.I enabled (which it is by default). With Catalyst A.I. enabled, all Direct3D games will default to ATIآ’s SuperTile rendering mode and all OpenGL games default to Scissor mode. ATI can overwrite one of these modes by implementing a profile in the driver that tells the cards to render in a different mode for any game. For example, if ATI finds that Alternate Frame Rendering (AFR) mode works best in DOOM 3, they can create a profile that sets this mode when you launch the game. ATIآ’s driver profile implementation is very similar to NVIDIAآ’s SLI implementation. NVIDIA determines the best modes for each game sets a default driver profile for each game. The difference here is that ATI has a default fallback-rendering mode if there is no profile. With SLI, you must manually enable multi-GPU mode.

There is a detailed description of all the rendering modes in our tech preview here. SuperTiling is ATIآ’s method of chopping the frame up into a checkerboard pattern where one card renders one tile and the other card renders another tile. The Scissor mode of rendering, which is the same thing as NVIDIAآ’s Split Frame Rendering (SFR), where the frame is split in half. AFR is a method in which one video card renders one frame and the other video card renders the other frame. AFR, for the most part, will provide the most performance since it also scales geometry.

Beyond that, ATI also has a new mode called Super AA with CrossFire. What this allows is for higher anti-aliasing (AA) settings in games. For example, this is accomplished by having one card render 4XAA and the other card render 4XAA using different sample patterns. When you combine both of these to your display, you get true 8X anti-aliasing. NVIDIA also has an equivalent to this known as SLI AA.