Super n00b P55 PCIe Electrical Speed Question

gwar2288 · Oct 29, 2009

If I have a x16/x16(x4) Motherboard, can I get the both lanes to run at x8 somehow?

EarthDog · Oct 29, 2009

If you have 2 GPU's it will break down to 8x/8x...Otherwise...no. What do you require at 8x?

What motherboard do you have?

petteyg359 · Oct 29, 2009

EarthDog, some older motherboards (DFI Infinity P965-S) wouldn't split x8/x8, the second slot was only able to switch between x4 and x1, via a BIOS setting.

EarthDog · Oct 29, 2009

Yep... but this is P55 with the controller on die. Different story I would imagine..No? (see title of thread)

gwar2288 · Oct 30, 2009

It would be 2 GPUs yes.
The reason I ask is because I have a GA-P55-UD3 with an ATi 5850 atm, (Running in the x16(x16) lane) and it has a 2nd PCIe x16 slot, but it states x4 electrical.

I am not too fussed either way (from what I can gather the performance hit is only 5% or less), but just wondering

EarthDog · Oct 30, 2009

With the 5850, a slower card, you may not see any performance decrease that was shown with a 5870 in 8x as the 5850 is more than the 1-2% slower than the 5870.

gwar2288 · Oct 30, 2009

EarthDog said:
With the 5850, a slower card, you may not see any performance decrease that was shown with a 5870 in 8x as the 5850 is more than the 1-2% slower than the 5870.

I understand that

My Question was mainly curiosity about whether crossfire would run at x16/x4 or at x8/x8.

EarthDog · Oct 30, 2009

After reading a bit more, Im not sure I provided the right answer. I would suggest maybe PMing MIAHALLEN as he completed a review on this board and knows it pretty well.

Evilsizer · Oct 30, 2009

crossfire will run on 16/4 but not at the same level as say a 8/8. the 4x slot even being pcie 2.0 may hold back the second GPU.

EarthDog · Oct 30, 2009

Looks like PCIe2.0 4x is somehow only 5% loss...

http://www.techpowerup.com/reviews/AMD/HD_5870_PCI-Express_Scaling/25.html

Neuromancer · Oct 30, 2009

gwar2288 said:
It would be 2 GPUs yes.
The reason I ask is because I have a GA-P55-UD3 with an ATi 5850 atm, (Running in the x16(x16) lane) and it has a 2nd PCIe x16 slot, but it states x4 electrical.

I am not too fussed either way (from what I can gather the performance hit is only 5% or less), but just wondering

If it states 4X electrical than it will only be 4x. The board is not WIRED to handle 8x or 16x on the second slot.

the reason they still put a 16x slot in, is because, the pieces of plastic are cheap, and it saves them money not having to inventory too many different items. (plus allows you to run a second video card, even at reduced BW))

Super n00b P55 PCIe Electrical Speed Question

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