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Original Link: https://www.anandtech.com/show/3205
ATI has been particularly quiet regarding CrossFire since their launch at Computex back in June. I assumed that we wouldn't see CrossFire boards and cards until August or September at the earliest, and it's really starting to look like that's going to be the case. But I'm not here to talk about CrossFire availability, I'm here to talk about performance.
There have been a number of CrossFire previews published all over the net, including our benchmarks from Computex. But what truly caught my attention was the tests over at HKEPC that showed two X700 cards working in CrossFire mode with nothing more than a simple BIOS update, no master card needed.
Something about that just didn't make much sense; ATI went through all the trouble to stick a compositing chip on these CrossFire master cards, and all you really need is the BIOS from a master card? So we did some digging and Wesley actually discovered the truth behind current CrossFire performance.
ATI distributed a special driver to their partners prior to the Computex launch that was designed to simulate CrossFire performance, by only rendering odd frames (effectively doubling the frame rate and simulating AFR performance). Although we can't confirm that we also ran with this driver back at Computex, chances are we probably did. But more importantly, the reviews you've seen where a pair of slave cards are used aren't actually testing CrossFire, they are simply simulating the performance of CrossFire by rendering half the frames.
We have learned however that the performance of this special driver is actually virtually identical to AFR performance with CrossFire actually working, but it is important to understand that when CrossFire is eventually released - you won't be able to just flash the BIOS on a slave card and have it work as a master card. And obviously, you won't be able to use just any cards in CrossFire mode, you'll have to stick with a X850 or X800 master card.
Although I have yet to see final benchmarks, my guess right now is that ATI needs to actually release CrossFire when they've shipped R520 boards. Had NVIDIA not launched G70 it wouldn't have been as big of an issue, but with a single G70 basically equal in performance to a pair of 6800 Ultras, ATI isn't winning any brownie points by competing with yesterday's GPUs. I think a launch/shipping announcement of R520 and CrossFire either sequentially or simultaneously would put ATI's best foot forward, as CrossFire has lost a bit of its steam by this point.