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ATI unveils CrossFire

'More compatible than SLI', Nvidia-rival claims

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Computex 2005 ATI has indeed decided to name its multi-GPU graphics technology 'CrossFire', the company announced today when it launched the system as a more affordable, more compatible alternative to Nvidia's SLi.

As anticipated, CrossFire combines two ATI Radeon graphics cards, though only one has to directly support the technology. It had been suggested that the system could use any Radeon-based board as the 'slave' unit, but ATI revealed the list is more limited than that.

CrossFire will initially appear in two boards: the Radeon X850 CrossFire Edition and the Radeon X800 CrossFire Edition. The former will only work with other X850-based boards, specifically the Pro, the XT and the XT Platinum Edition models. Likewise, CrossFire-enabled X800 can take control of other X800 products, including the vanilla X800, the XL, the Pro, the XT and the XT Platinum Edition versions, and the X800 All-in-Wonder, ATI said.

This much-reduced list is still sufficient to ensure there are "almost a million people who are CrossFire-ready", the company added.

If they adopt the technology, they will see up to twice the performance of a single card alone, ATI claimed. However, the two boards can be combined for enhanced image quality thanks to their combined ability to provide 14x anti-aliasing - although you won't get the performance boost, ATI admitted.

And it all works with existing games, ATI said, contrasting CrossFire with SLi, which, it said, is only enabled in titles "profiled" in Nvidia's driver. While SLi uses a proprietary card-to-card connector, CrossFire uses the PCI Express bus. The video output of the slave card is fed into the CrossFire-enabled 'master' card, which drives the display.

CrossFire uses a tile-based rendering scheme, as expected. Each frame is divided into squares. The number of tiles allocated to each card depends on the relative rendering powers of the two cards. Tiles are supported by DirectX, ATI said, but not OpenGL. For OpenGL apps, Crossfire also supports a 'scissor' rendering scheme, in which the frame is divided laterally. The dividing line is again determined by the two cards' relative rendering abilities. CrossFire can also set the two cards to render full, alternate frames.

CrossFire will also ignore any pixel pipelines the slave card possesses beyond the number on the master card. Mix a 16-pipeline slave with a 12-pipeline master, and the two cards will both operate 12 pipelines apiece.

ATI said CrossFire configurations can be hosted by any motherboard with twin x16 PCI Express slots, but it suggested mobos based on its own Radeon Xpress 200 CrossFire Edition chips would provide the "optimal" gaming experience. Asus, ECS, Gigabyte, Tul, MSI, Sapphire and DFI will all offer CrossFire Edition mobos later this month for both Intel and AMD processors, ATI said.

Radeon X850 CrossFire Edition cards will ship in the middle of July, it added, with Radeon X800 CrossFire Edition boards appearing early August. ®

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