AMD Quad-CrossFire - CrossFireX Performance Preview
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An Introduction to CrossFire X technology
It's rather funny that until today, the technology behind CrossFireX was really supposed to be some kind of secret. The idea of plugging in more than two GPUs into a multi-GPU system for AMD/ATI is actually brand new in the modern hardware era. Ever since we first saw ATI graphics boards with pairs of CrossFire connectors on them we were told to expect the ability to scale with three and four cards in the future. The only problem was the future just never caught up to us. Until now that is.
We have chronicled the recent news and rumors about CrossFireX and the ability to pair up several graphics boards in a single system for some time. There have been interviews with AMD staff, the news about the upcoming RS780 chipset and hybrid graphics as well as our own revelation that CrossFireX would be working on Intel's Skulltrail platform while NVIDIA's 3-Way SLI would not. Even in our review of the Radeon HD 3870 X2, AMD teased us with the "coming soon" insignia of 2 Teraflops of GPU computing power.
But have no fear faithful AMD fans, the CrossFireX driver is merely weeks from a public release and we were given the chance to test it out for ourselves. Read and enjoy.
AMD CrossFireX in Brief
CrossFireX technology is really simple in theory: take two, three or four GPUs and use their power to render one game faster than you otherwise would be able.
AMD is the first GPU company to attempt to make multi-GPU technology as forgiving as possible. What do I mean by this? Simply that AMD is trying to get rid of the hard coded restrictions that NVIDIA and their SLI technology place on gamers and what hardware they can use together. You can only use same-GPU graphics cards for example, on both SLI and past CrossFire platforms. That is changing; here are some of the most interesting bullet points that AMD is bringing to enthusiasts:
- Pairing of two Radeon HD 3870 X2 cards (two GPUs on one card) for four GPUs
- Pairing a single Radeon HD 3870 X2 with either an HD 3870 or HD 3850
- Combining up to four RV670 cards of any kind or speed: HD 3850 256MB, HD 3850 512MB and HD 3870 512MB for improved performance
This obviously left me with lot of questions as to performance, compatibility, etc. AMD was kind enough to answer these questions for me today.
Q&A with Catalyst lead Terry Makedon
PCPER: How flexible can the CFX software be in terms of pairing different GPUs together?
PCPER: How does CFX work with card with different size frame buffers like a 3850 512MB and a 3850 256MB?
PCPER: Why does DX10 have more trouble working with 4 GPUs than DX9 does? I thought there was a DX9 limitation to frames rendered ahead originally?
PCPER: What are you all doing to address the issue of “lag” in games where the game is “thinking” and rendering up to 3 frames ahead of what the gamer is seeing? 3 frames doesn’t seem like much but in a game that is running at 30 FPS, that might become an issue. In the cases where the driver has to “throw away” frames because one of the frame took longer than expected to render, is anything adjusted there?
So it's clear from these answers that there isn't any magic potion that AMD is using to get CrossFireX working as they have: just a lot of work and testing. And the same problems or issues that were found when mixing cards in previous generations are basically still here: your system will only have the POTENTIAL to work as fast as your SLOWEST graphics board multiplied by the number of GPUs.
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