All-new hardware

In case you aren’t familiar with how CrossFire works, we will very briefly go over the CrossFire basics. For further information, we highly suggest you check out our CrossFire Performance Preview and Computex 2005 stories from earlier this year.

Since ATI’s Radeon boards don’t have a native way to communicate with one another, ATI has had to integrate a number of chips to handle the communication and compositing necessary for CrossFire to function. This collection of chips is known as the compositing engine and is found only on CrossFire “Master” graphics cards. The compositing engine on the CrossFire card takes the partial image from the “Slave” graphics card and combines it with the other half of the image from the CrossFire master card. Once the images are combined, the final result is then sent out to your monitor. With each card’s workload cut in half, performance is improved. In fact, in a best-case scenario, performance should nearly double.

The Radeon X1800 XT CrossFire pictured with GeForce 7800 GTX 512MB

The CrossFire X1800 XT config

Enhanced compositing engine

For the Radeon X1800 CrossFire board, ATI has improved the compositing chip, replacing the old Xilinx Field Programmable Gate Array (FPGA) found in the original Radeon X850 CrossFire with a newer, more powerful Xilinx FPGA. ATI claims that this new chip is faster than its predecessor, and is also more programmable. In theory, the new compositing engine can be reprogrammed to deliver enhanced performance, compatibility, or functionality in the future.

In addition, the new FPGA has been designed to handle the blending used for CrossFire’s Super AA mode. According to ATI, with the compositing engine handling hardware blending, the huge performance hit normally associated with Super AA is largely mitigated. In fact, as you’ll see in our Super AA testing, you’ll see that thanks to this feature Super AA is nearly free in some cases. In laymen’s terms, this means that you can turn on Super AA and see practically no performance penalty.

CrossFire X1800 XL config

The CrossFire board meets the Radeon X1800 XL

Addressing the 1600x1200 limitation

Without a doubt, one of the chief criticisms leveled at ATI’s Radeon X850 CrossFire board was its lack of support for mega high resolutions. Radeon X850 CrossFire boards were limited to just 1600x1200 at a headache-inducing refresh rate of 60Hz. Fortunately, ATI has integrated two dual-link TMDS transmitters for DVI into the Radeon X1800 XT, much to the delight of Apple 30” Cinema display users.

The move to dual-link transmitters also has huge ramifications for Radeon X1800 CrossFire. With a dual-link interlink, DVI bandwidth is doubled, providing resolutions of up to 2560x1600. Previous ATI Radeon offerings relied on single-link DVI transmitters.

Other than these changes, the rest of the technology found in ATI’s Radeon X1800 CrossFire card carries over unchanged. You’ve got the same rendering modes (scissor, supertiling, and alternate frame rendering) and the same Super AA modes. As a member of the X1800 family, the Radeon X1800 CrossFire supports ATI’s new transparency AA feature, as well as ATI’s Smoothvision HD anisotropic filtering.