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Crossfire: 8x vs 16x and Data Throughput

Last response: in Graphics & Displays
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April 25, 2010 1:11:35 PM

Hi, I have two questions regarding a possible Crossfire setup.

My setup:
ASRock M3A780GXH/128M
Phenom Be 955 @ 3.2 Ghz
HD 4890 1GB (It's the Sapphire Vorpex ehanced someting)
My resolution is 1920x1200

I want to add a second 4890 card to the setup.

(1) The Board supports 3x Crossfire, with a 16x, 8x and 4 slot respectively. I couldnt find a comprehensive overview of performance scaling in 2 card crossfire, but the consensus seems to be that the loss between full 16x crossfire and 8x crossfire is insignificant. Does anyone have more information about this? Will a second card yield a significant performance leap in games?

(2) Will my cpu/mainboard be fast enough to load 2 cards? I read sometime, somewhere that the Phenom architecture (or was it the bridge design on the board?) can't support hi class sli/crossfire setups. I don't know at which level of graphics card this problem starts and if it's only relevant for triple crossfire.

I'm happy for every information/link you can provide.

Thanks,
rl70
a b U Graphics card
April 25, 2010 1:30:17 PM

(1) A x16 slot can only approach saturation with 5970s, and to a lesser degree, highly Oc'd 480s and 5870s. CF 4890s are close performance wise with an OC'd 5870. x8/x8 CF will not hinder the performance boost of adding a second 4890 compared to x16/x16 on identical platforms.

(2) There is a difference between scaling efficiencies on AMD Phenom II setups when compared to i7 x58 builds. The i7 rigs will give a bigger performance boost from adding a second card, but the real difference in these platforms is seen with multiple 5xxx cards, and setups with more than just 2 cards. When it comes to crossfiring 48xx cards, the differences between Phenom II and i7 multi-card scaling efficiencies is much smaller.

To sum it up, you should not be dissappointed with the addition of a second 4890 on your current setup, provided you have the PSU to handle the second card.

You will see even more of a performance boost, CF or not, with a bit of an OC on your CPU. AMD BE chips are pretty simple to OC, and even just a small boost to 3.6ish would yield better performance. Just a suggestion, though even at stock speeds you have a great gaming platform.
a c 177 U Graphics card
April 25, 2010 2:31:05 PM

And just to prove the point:

http://www.techpowerup.com/reviews/AMD/HD_5870_PCI-Expr...

At that res, I would also say a second card would be a good idea, just remember that not all games scale well-and some not at all-with CF or SLI.
Overclock, you know it makes sense :) 

Off question: You might be better served E-baying the 4890 and swapping it for a HD5850 rather than going the CF route with two 'outdated' DX10 cards.
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April 25, 2010 3:44:53 PM

First of all thanks for your great replys!
I went a little tight on the psu. I calculated OCed Phenom and 2 cards and 10% PSU loss and I came to 480 Watts with my system. I bought a 550Watt quality PSU (Some brand name, I can't remember right now). I gonna investiage that further.
I got the idea to plug a second 4890er card, because I think I can get one on ebay for around 70e.
Another thing I left unresolved is that I have some bootup issues. Soemtimes when I start my pc, screen doesn't turn on and the pc doesn't boot into windows as far as I can tell. It was worse when I used EZ Overclock in the bios. I had to reset my cmos on the mainboard. Now it runs fine, I have to investigate this stuff further if I think of upgrading/overclocking.
I bought a coolermaster cooler for my cpu and I have 2 tower fans, but my approaches to overclocking failed so far. I couldnt get it stable even on just more than 3.4ghz. As far as I can tell it overheated. I don't really know where the problem is.
a c 177 U Graphics card
April 25, 2010 5:38:20 PM

Sounds very much as if the PSU cannot handle the loads abd you'll need a good 650W unit if you plan on Crossfiring the HD4890 AND overclocking.
I like Coretemp or Speedfan to check the CPU temperatures and you may also be able to set a temperature alarm in the motherboard BIOS for additional safety.
If it is overheating, try reseating the cooler and usung a premium thermal paste like Arctic Silver 5 (AS5) and check the fan is working.
April 25, 2010 7:36:43 PM

So, I just looked it up. I bought the OCZStealthXStream 600W Atx2.2. At least with the current configuration is shouldnt have a problem. When I use a generous calculation here (http://www.thermaltake.outervision.com/) it tells me I need 514 Watts. So overclocking should definetly be in. I actually bought a special thermal paste and I bought some cooler master cooler.
April 25, 2010 7:38:11 PM

About the second CPU. I guess i rather wait another half a year and change my hd4890 with some newer graphics card. definetly cheaper than buying a new PSU (also calculating the energy cost).
!