Ati Crossfire Performance (Dual X16 vs X16/X4)

Tordek

[H]ard|Gawd
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Here's a question for you guys:

Say I'm choosing between these 2 motherboards:

Motherboard A has Dual X16 PCI-E slots for crossfire and its supported from the chipset reference design.
(Think AMD 790FX or similars link)

Motherboard B has 1 X16 and 1 X4 PCI-E slots for crossfire and the chipset does not support crossfire from reference but the manufacturer added support thru their design.
(Think the modified AMD 785g by ASUS that was recently reviewed at hardocp.com link review link)


What would the performance hit be (if any) should I decide to use crossfire on Motherboard B versus Motherboard A?
 
Ouch, could be a lot on a powerful card. Will x16 cards even work on a x4 slot?

If you're going to invest in crossfire the 2 cards, the more powerful PSU the more cooling etc, it would be worth doing it right and getting a true 2x16 slot motherboard, make sure to check they both run at 16x at the same time also, some cheap ones wont.
 
Jetway sounds like a Jacuzi Brand rather than a Motheboard brand imo.
(could be way off since Ive been out of the scene for a while though)
 
at x16 by x8, the first card gets full bandwidth, and pretty much so does the second, so i can infer that at x8, the card will run fine. but at x4, i am guessing it will fun half the power, so i wouldn't recommend it.
 
Gotta agree, if you know you are running crossfire get a board that will do at least x8 / x8. Running a high end card at x4 is scary.
 
Jetway sounds like a Jacuzi Brand rather than a Motheboard brand imo.
(could be way off since Ive been out of the scene for a while though)

Don't worry, JetWay is *sometimes* decent, but too many times then not, crap.
 
The hit will probably be significant. 8x/8x will be fine, but 16x/4x might be pretty rough.
 
x16/x16 = 2560x1600
x8/x8 = 1920x1200/1920x1080

basically dont worry about your cards running in 8x/8x unless your gaming at 2560x1600+, but x16/x4 is definitely not good.
 
I read some more articles and the results are not nearly as dramatic as they were in the tweaktown benchmark.

AnandTech wrote an article that was a good read, as I said, the results were not nearly as dramatic. But in games like crysis when you only avg 30fps on very high with CF 4890s, 5fps can make a big difference.

All i5 compatible boards will do the x16 split right? Its a core difference between the i7 and i5 architecture?
 
the performance hit on x4 pcie vs 16x pcie is about 10-20 frames/s, on 8x vs 16x about 5 frames/s. there`s a site testing various bandwith configs, but I forgot which one it was.
 
This is pcie 2.0 right? Then don't get x4 if you plan on using cards better than an 8800GT. Cards faster than that need more.
 
Think of it this way,

16X = Shelby Cobra on a 4 lane freeway with no traffic
4X = same car on a one lane dirt road.:eek:
 
I wouldn't buy a 4x PCI-E board for SLI or X-Fire. It's been shown in benchmarks that you need 8x for modern gpu's full performance, but anything more than that doesn't do much of anything for you, especially in a dual gpu setup where your not 100% utilizing each card anyways.
 
Well, if you look at what I use......

I have 16X lanes for both my GPUs.
Most Crossfire profiles use alternate frame rendering.
Depending on the game, when I pull up my MSI Afterburner software, the GPUs are hitting between 90 and 99 percent when the 3D is very demanding............

I think at this point, the cards are getting close to being hand-cuffed by 8X lanes.....in very rendering intense scenes. I don't have anything scientific to base this on.....just what I see in my own use.
 
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