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Two PCI-E cards, not SLI/CrossFire

Last response: in Graphics & Displays
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May 17, 2008 12:21:22 AM

My motherboard supports two PCI-E cards, with only one slot being used currently. I have an 8800GTS (EVGA 320) in one slot and would like to add another card here soon (for the curious: EVGA 8800GTS 512).

I'm not interested in SLI, so I won't be working with that.

My question is, if you're using SLI, the PCI-E slots will run at 8x, but what if you're running two cards, not in SLI? Will one card be 16x, the other 8x or, because both slots are used, will they both run at 8x?

I feel like I should have found the answer for this without asking (so forgive me if I've overlooked the thread), but everything I've run into deals with two cards of the same time in SLI/CrossFire.

Thanks for your help.

More about : pci cards sli crossfire

a b U Graphics card
a b V Motherboard
May 17, 2008 12:29:36 AM

The PCI-Express modes are the same for using two cards separately as they are for using two cards in SLI. SLI is done by the graphics DRIVER (software), not the motherboard.
May 17, 2008 12:44:58 AM

So then if my motherboard documentation tells me that running two cards "in SLI" will cause the both cards to run in x8 mode, then regardless of whether or not they are actually in SLI, I will have two cards in x8 mode? I'm only able to find documentation for "two cards in SLI," not "two cards."


Here might be a better question, one that will give me an answer closer to the heart of things:

Is it standard for two PCI-E cards to run in x8 mode, regardless of motherboard?

Or is it up to manufacturer to build a board that that has two x16 mode slots (and sometimes to cheap out/whatever they make one slot operate in x8 mode and the other in x16 mode)?
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a b U Graphics card
a b V Motherboard
May 17, 2008 12:49:43 AM

If the documentation says two cards run in x8 mode for SLI, two cards will run in x8 mode regardless.

Getting to the larger question, it all depends on how many PCI-Express lanes your chipset supports and how the motherboard manufacturer directs them. If you have, say, 20 lanes, you'll likely have one slot in x16 mode and the other in x1 mode by default, switching to two in x16 mode and disconnecting the x1 pathway when two x16 cards are installed.

The rest of the x1 pathways go to either x1 slots, an x4 slot, an x8 slot in x4 mode, an x16 slot in x4 mode, or onboard devices, depending on motherboard design.
May 17, 2008 1:21:47 AM

Would be nice to have additional information before commenting, what motherboard are you using, and are you planning to run 3 or 4 monitors, I assume this is the case since you say you aren't interested in SLI mode.
May 17, 2008 2:04:51 AM

Thanks for all your replies.

With regard to rgsaunders' statement: http://www.newegg.com/Product/Product.aspx?Item=N82E168.... An ASUS M2N-SLI Deluxe. The manual suggests I put my video card (when using only one) into Slot A, due to the fact it runs in x16 mode.

Right now I only have two monitors, but I plan on getting a third eventually. The reason for a second video card at this point is to upgrade my (mild) gaming. I figured I'd run display 1 on the new card, display 2 on the older card until I got a hold of my third monitor, at which point I'd decide how to best use the third displays in my workflow and attach the video card to the display it best compliments.


May 17, 2008 2:27:55 AM

Newegg link says "PCI Express x16 2 x PCI Express x16 slot at x16, x8 speed
Support NVIDIA®SLI™ technology (both at x8 mode)"

Nvidia docs say 8x for both slots with SLI.

I'd say if not running SLI you'd get 16x. But I don't think you'll notice much difference than if it were 16x.

May 17, 2008 2:51:21 AM

Thank you, firebird, for a) referencing the nvidia docs and b) taking the time to reference the nvidia docs. I guess I was/am a little confused by the wording. Luckily, none of my tasks are "mission critical" and, as a result, you're right: I probably wouldn't much difference. :) 
a b U Graphics card
May 17, 2008 3:27:39 AM

You are correct, you wont notice a difference. Your motherboard doesn't have enough PCI-E paths to run both slots at 16x, it is electrically impossible. If the manufacturer could run them both at 16x, they would. That's why the 680/780 and 975/x38 chipsets exist, they have more PCI-E paths to allow for dual 16x mode. In a few years, the mainstream boards will too, just not yet.
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