ATI CrossFire Multi-GPU Technology Preview
Introduction to ATI CrossFire Technology
At this year's E3 show ATi was discretely showing their new multi-GPU rendering technology which until now has been held under wraps of the standard NDA embargos we've come to know and love here in the industry. Last week we were given a full briefing on the technology by the ATi team and were told sometime in the month of June, product should be available in the retail channel. However for now, we can give you full details on the features and underlying technology in ATi's new CrossFire products with this pre-launch showcase, which we will follow-up of course, with a full performance preview once we get product in our lab for hands-on testing.
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|Intel LGA775 Reference Board
|AMD Socket 939 Reference Board
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Crossfire Enabled X850 XT:
Notice The Upper Connector
Radeon X850 XT x 2:
Dual X850s Installed
The three components of ATi's CrossFire solution are the following: A CrossFire-ready ATi Radeon Xpress 200 Motherboard, a CrossFire Edition Graphics card of the "same series" of GPU, and a Radeon X800 or X850 series PCI Express Graphics card. There are only a couple of options for CrossFire based cards which does limit users a bit within the same GPU family. More on this later.
To enable multi-GPU rendering ATi had to "roll their own" ASIC specifically dedicated to image composition. This device is an FPGA (Field Programmable Gate Array) that does add some cost to the card for sure but it also allows ATi to provide updates potentially via firmware in the future. The compositing engine is responsible for assembling the final image from each GPU before it goes to output. Finally, the compositing engine chip will only be installed on CrossFire enabled cards and the other Radeon X800 series card that is installed doesn't have to be a CrossFire based version.
Very few calls sent over PCI Express -
Also as you can see here, there is no PCI Express link connector between the two graphics cards. Instead we see a split DVI/DMS combination cable that transfers most all calls between the GPUs via the compositing engine. (Incidentally, this cable also allows for dual DVI connections off the main card, since the splitter also breaks out another DVI connector. ) There are still some cases where certain operations may go out over PCI Express but these cases are rare supposedly, as explained to us by the folks at ATi. A render-to-texture operation is an example of a call that would go out over PCIe but in general there is very little PCIe bandwidth consumed with ATi's implementation, which on the surface, with it's external cabling, could look a bit like 3dfx's SLI of old. However today's CrossFire certainly is nothing of the sort.