ATI CROSSFIRE TECHNOLOGY

ATI CrossFire platform consists of:

1. ATI RADEON XPRESS 200 CrossFire Edition core-logic motherboards
2. ATI RADEON X800/X850-series graphics card
3. ATI RADEON X800/X850-series CrossFire Edition graphics card equipped with "Compositing Engine"

A special chipset that is called the "Compositing Engine" blends parts of frames rendered from two different graphics cards. The CrossFire Edition cards contain a chip called the "Composition Engine", which receives data from a regular Radeon X800 class video card via a DVI input. The chip then merges the data and sends the final output to the monitor.

The Radeon X800 CrossFire Edition cards can be paired with any PCI Express Radeon X800 graphics card (Radeon X800, Radeon X800 PRO, Radeon X800 XL, Radeon X800 XT or Radeon X800 XT Platinum Edition) from ATI or any of its partners. Because of the backwards compatibility of the platform, there are already a million pluses customer whose are CrossFire Ready.

The CrossFire compositing engine is a programmable chip that offers flexible support of different graphics cards, allows a superior feature set (advanced compositing modes), and enables further enhancements to be quickly implemented on next generation products. The CrossFire compositing engine also offers a performance benefit over combining the final image on the GPU.

• CrossFire can enable multi-GPU rendering on all applications.
• CrossFire supports Supertiling which evenly distributes the workload between the two GPUs to improve performance. CrossFire can use multiple GPUs to improve image quality rather than performance with Super antialiasing (AA) modes. Supertiling is only supported on the CrossFire platform.
• CrossFire is an open platform that supports multiple components and graphics cards that can be mixed and matched in a single system.

The new motherboards and video cards will be available in August or September. In August the next Intel 955X chipset will have the CrossFire technology enabled on the chipset so it will be able to work with the ATI CrossFire Edition video cards.

Only the X1900 series chipset comes with the cable for the CrossFire to works and the X1300, X1600 and the X1800 does not comes with the cable for the CrossFire. For these chipset it will be driven by the drivers to enable the CrossFire to works.

• Supertiling — The screen is split up into 32x32 tiles and the workload is distributed according to a checkerboard-style pattern, with one card taking what would be the blue squares and the other the squares that would be red. Splitting up the workload in such relatively small tiles should result in a distribution of the load that's very close to an even split, and it should allow two cards to produce markedly higher fill rates and pixel shader throughputs than a single card. The vertex processing load will be duplicated on each card, however, so that a CrossFire system with supertiling won't likely achieve any higher geometry throughput than a single card. Supertiling will be the default CrossFire mode for all Direct3D applications, but will not work in OpenGL.

   

   

• Scissor mode — This mode will be familiar from SLI, where NVIDIA calls it split-frame rendering. Scissor mode divides the screen horizontally, giving the top portion of the screen to card A and the bottom portion to card B. The exact proportion of the split is adjusted on the fly as workloads change. This will be CrossFire's default mode for OpenGL and will also work in Direct3D.

  

   

• Alternate frame rendering — This one, ATI reminds us, is the mode used by its previous multi-chip solutions, like the Rage Fury MAX. Alternate frame rendering involves buffering a few frames ahead of what's being displayed onscreen, with the cards alternating drawing entire frames. AFR can be enabled on a CrossFire system via ATI's control panel. This mode distributes both fill rate and geometry loads evenly between the cards, allowing for better scaling. ATI says AFR should be an option for both OpenGL and Direct3D applications.

  

   

• Super antialiasing — Uniquely, CrossFire rigs may provide image quality benefits even in games where fill rate and geometry throughput isn't normally at a premium via its Super AA capability. Super AA comes courtesy of the CrossFire compositing chip, which can combine images with different sample patterns produced by the two cards. CrossFire AA offers several new antialiasing modes from 8X up to 14X. 8X and 12X AA modes double up on 4X and 6X multisampling, respectively. 10X and 14X AA modes, on the other hand, combine 2X super sampling with 8X and 12X multisampling, respectively.