Bandwidth Question....Please Help.

[Briggsy]

Hi All,

I'm running 2x 7970 crossfire as my sig would suggust and their running in slots 1 & 2 of my mobo, this configuration puts the cards very close togther and is making my top card over heat when overclocking......

So I would like to move one card to slot 3 with a long ATI cross bridge so then the config would be slots 1 & 3, would there be any reduced bandwidth issues, I have linked my mobo below so you can see the settings for each slot in detail.

If anyone could help I would be most grateful?

http://uk.asus.com/Motherboards/Intel_Socket_1155/P8Z68V_PROGEN3/

Thanks

 

[Ciric]

You are not gonna like the answer, but yes.

The buttom x16 slot, is only wired as a x4 slot + it goes to x1 when you enable the onboard USB 3.0 header, the Esata or the top x1 slot.

You are in kinda of a bad spot, with those two cards in CF when you wanna oc, since they just dump the heat in the case. My sincere advise would be to either go liquid cooling, or accept the stock speeds.

 

[dugdiamond]

*2: The PCIe x16_3 slot shares bandwidth with PCIe x1_1 slot, PCIe x1_2 slot, USB3_34 and eSATA. The PCIe x16_3 default setting is in x1 mode.

^^^ without placing extra fans, blowing between the gpus, the only other solution would be watercooling

 

[Ciric]

#3

Yea, and as said you can get x4 speed by diabling those things.

All in all, #0 will only get a max bandwith of 4 lanes pci express 2.1 wich will limit him, (and require him to disable the slot in wich he has a soundcard). This is the biggest letdown compared to the deluxe boards, wich has a plx chip to share the bandwith.

 

[Briggsy]

Thanks for your answers guys, which board can you recommend which will enable me to maximize my GPU capacity whilst keep my GPU's far enough apart to keep them cool?

Thanks

 

[Big WigglyStyle]

Just wondering, would the bandwidth make that much of a major difference in FPS/Performance? Before you go and buy a new motherboard perhaps try this and see if your performance takes a hit?

 

[Briggsy]

This is what I'm wondering......what you reckon guys?

 

[Master&Puppet]

pcie3 x16, x8 and pcie2 x16 = full gpu use

pcie2 x8 (pcie3 x4) = occassional bandwidth saturation resulting in up to 15% fps drop

pcie2 x4 = typically 5-40% fps drop.

http://www.anandtech...ocking-and-msaa

 

[Briggsy]

Thanks M&P - so how would that scale with my original question?

Thanks

 

[Ciric]

You would go all the way down to PCI express 2.1 x1 because you use one of the x1 slots for the Xonar. IE you would see a MAJOR loss.

 

[Master&Puppet]

Yea you'd take a big hit putting the second gpu into the black slot (pcie2 x4 I believe). I'd venture to say that you are better off limiting your overclock to get both cards running in the x8 lanes rather than one card with a full overclock and the second completely strangled by bandwidth. Being honest - as much fun as it is having overclocked 7970s - you have 2 so even at stock we are talking major fps.

 

[Big WigglyStyle]

Ah, thanks for explaining that.

 

[SubTract]

if you have a place for a fan on the side of your case I would simply put a fan pulling air into the case pushing cool air directly to the graphics card/s. otherwise you could simply lower your clocks a little.