CrossFire Scaling Analysis
While a two-card CrossFire configuration generally benefited the P55 platform almost as effectively as it did the X58-based platform, we saw mixed results with a third card added. Poor bandwidth on the P55’s third slot caused triple-GPU performance to actually go down in some benchmarks, dipping below the dual-GPU and occasionally even single-GPU results. Yet, by adding in a few successful benchmarks, a chart of average performance doesn’t reveal this weakness.
Looking only at averages, the chart above makes it appear that adding a third card boosts P55 performance by nearly 8%. Yet the fact that it hurts performance in some games and offers no benefit in a few others means that we’d never suggest using the P55 PCH to host a third graphics card in CrossFire or SLI. Moreover, the X58 gains 25% by adding a third card and has no performance issues, with the exception of the well known Crysis “2560x1600 plus AA” multi-GPU bug, likely caused by our cards running out of frame buffer.
We again see that this particular X58 motherboard is slightly slower than this particular P55, as demonstrated in the single-card tests, and we refer back to its earlier review to prove that the difference is limited to this specific motherboard model. Yet, even though our motherboard of choice is slightly slower than many others, its dual-GPU CrossFire configuration provides 4% better performance than the P55 with identical graphics.
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I wonder does the same go for 790gx vs fxReply
I just ordered myself an ASUS P7P55D-Pro and didn't understand the difference... If I spent $1200 on video cards to go in this bad boy expecting it to test at higher performance that I will never be able to see by the naked eye it may have been a bigger deal(but it isn't).Reply
It is pretty logical to go the X58 route if you are planning for more than 2 cards...Reply
Only 2x HD 5970s would have significant bottleneck with x8x8 config of the P55...for rest of the cards, the x8x8 still would suffice...
For most of us, it looks like the P55 is the way to go for a gaming machine. I was a little surprised at how well two X8 channels did.Reply
Does it make a difference for the motherboard wether or not all slots are populated when we talk energy? Each pcie plug is supposedly able to deliver 75W to the cards right? so at 3 cards that's quite a bit of power. In addition it has to deliver what, 140W? to the 4ghz cpu .... remembering an earlier article detailing failed boards because of inadequate vrm's I just have to wonder if a higher power draw on the pcie connectors would make a difference in sustainability with such an oc? I mean at some point I would assume a board can draw more power than the atx connector or the power plane can handle?Reply
pcie 2.0 supports up to 300w (1.1 was 75w). The 5870 draws about 170w at load. This was the reason the 5970 was scaled back to 5850 speeds. Overclocked 920 @ 4.0 is going to draw about 250w. i5 750 (@ 4.0) on the other hand draws about 150w.Reply
For awhile now it's been known that the p55 will run an 8x8x crossfire within close proximity of it's x58 16x/16x even on 5870's. The only real question that hasn't been seen is the quadfire 5970's and a trifire 5970+5870. Publish that and you'll garner my attention at least.
300w ? but why then would new cards still ship with pcie6 and 8 connectors if the cards actually could make do with the pcie supplied power? I mean, sure for pcie1 support, but won't they still bitch if one was to not plug em in under pcie2?Reply
ps. 150W is also a lot for a processor designed for two digit numbers. Is there some kind of list somewhere of which motherboards support how much vrm power, or how many phases generate how much wattage or whatever can be used as a guideline?
Gonna upgrade the p35 to p55, and I've never been one for stock speeds...
The gap is just going to increase with more and more powerful graphics cards. We're talking 1-2 years and 8x will be performing just like 4x is now.Reply
8x Pci-e lanes should now be considered a drawback when purchasing new hardware.
"8x Pci-e lanes should now be considered a drawback when purchasing new hardware."Reply
They just proved it was NOT a drawback with two 400 dollar top tier gpu's.
Someone that advocates not upgrading the rest of their motherboard specs to the current high performance components such as DDR3 and the fastest hypertransport speed should not worry about THEORETICAL pci-e bandwidth.
Yeaaaaah! I've been waiting for this article for quite a while now, this clears up a lot of speculation! I hope you guys do a follow-up article to test whether two 8x,8x are enough to support 2x 5970's....Reply
If this article had come out 2 weeks ago, I would have upgraded to an i7-870 and 2x 5870's, but now that we know Fermi is arriving in Q1 2010 I'm afraid i'm gonna have to wait. . . again -.-
Oh well, that's why we love the PC market, always advancing :)