problem with two 9800gx2


I have the following configuration in my PC.

Primary PCI-E 16x : 9800gx2 card1
Second PCI-E 16x : 9800gx2 card2
Motherboard: No SLI support and no overclocking.
PowerSupply: Antec Quattro 850W (certified to work in Quad SLI mode).

I am able to boot the PC with only one of the 9800gx2.

If I give the power supply to both the 9800gx2 then the PC does not boot
and the usual blue light in the geforce 9800gx2 card is absent.

Can you suggest if I am overlooking something in this process ?

Your help will be really appreciated.


This sounds like your power supply isn’t sufficient for both cards simultaneously.

But the power supply that we currently have

is quad sli ready and shoud’nt 850W be

enough to drive two geforce 9800gx2 cards ?

Even if I connect another low-end graphics

card in the primary slot instead of gx2 card

the PC is still not able to boot properly.

Any other changes that I need to do in

the configuration ?

Which motherboard you are using? Which chipset? How many PCIe 2.0 16x slots your motherboard has? Are all of them at 16x speed?

As I know, GX2 cards (from gigabyte) have LED indicators around SLI connectors and you will see those LEDs light red if their power is a problem. So power is probably ok.

Check documentation of your motherboard for all PCIe slots. I’am not sure does GX2 work in non 16x slot.

Motherboards: ASUS P5W DH Deluxe

2 x PCI-Express x16 slots (PCIe 1.0)

The motherboards supports two PCIe slots and according

to the manual I can connect two PCIe graphics card.

Perhaps this an SBIOS bug. You’d likely be best to contact Asus. This doesn’t seem to be a CUDA problem.

If I am reading this correctly you are trying to run Quad SLI on an Intel mobo ?

Thats not possible because its an ATI Crossfire board & altho you can have SLI with GX2
it only works with one of them so you cannot have two seperate cards working in unison
unless they are ATI

9800GX2 contains two cards fitted together inside it’s case with a SLi bridge

No, he is not trying to do SLI :)

well why is he trying to run with two cards in the slots? what is the point if they won’t work together?

If you look upstairs, these are the CUDA forums. CUDA sees each device as a separate device, and you need to address each device separately. This is not about gaming ;)

It would be helpful if you can elaborate on this.

Mr. Riedijk is Right. I want to run the system in multi-GPU mode without SLI.

Hence in the end the CPU should see four CUDA enabled devices.

Right now the booting process itself is failing when I plug in two GX2 cards.

One of problems could be,
as you said you are not using SLI. But how do you know that? You think it is enough to leave SLI adapter disconnected and cards are not in SLI mode?
That is true only if you are using cards with single GPU. But GX2 has two GPUs and has some kind of adjustable built in integrated SLI adapter (off course it has an external SLI connector too allows it to connect to other cards). Adjustable means you can manage SLI connection through software (turning it on/off) between those two GPUs on single GX2 card. Offcourse it is adjustable when you start nvidia driver installation under windows but until that, during PC powers on, BIOS should properly interpret it. But it seems BIOS doesn’t do that on right way.
As you probably know, nvidia reserves all rights for multi GPUs platform working in SLI with more than 2 GPUs. It means three or more GPUs in SLI mode could run only on motherboards with nvidia chipsets. Off course you plan to work on CUDA in only possible non SLI mode (if you want all GPUs are visible to CUDA) but maybe BIOS doesn’t see that as you do.

Contact ASUS support center. BIOS update could solve problem.

Also, I’m curious, did you buy all components together or you already had motherboard? If components are new I would replace motherboard (or smash it on dealer head because he didn’t warn you about possible problems) For an extra cache on your board price you can buy PCIe 2.0 motherboard with nvidia chipset and get full performance from your GX2 cards. If you are not using water cooling system then increase that extra cache for a price of an extra case fan. (Just trying to save you go twice in the store)

Hey thanks for the reply.

I am plugging in these gx2 cards into my existing PC with a non-sli

motherboards having intel chipset.

I was trying to quickly build a quad gpu system with my existing setup.

As far I can understand from the existing reply it could be a BIOS

problem and I will try to contact ASUS support.

Problem being that inserting a GX2 introduces Sli regardless of whether you want it or not hence the failure of his mobo to fire up with more than one inserted.

SLI is a driver thing, so failure in booting has nothing to do with it.

SLi is also a hardware thing, the Intel mobo can’t accept the four cards inserted in two slots ,thats why he can boot with one inserted but not with both, or indeed with any other second card by the looks of it

which would be a BIOS bug ;)

There is nothing hardware-related that prevents it, just a BIOS that does not do The Right Thing ™ :D

I think EDR is right, it does smell like a BIOS issue.

But one explicit test first. Have you tried booting with each card seperately?

you say “I am able to boot the PC with only one of the 9800gx2” but that may not be enough tests to rule out a card problem. If card 1 is in slot 1 and card 2 is in slot 2, can you boot the machine successfully with JUST card 1 in slot 1? And if so, as a second test, can you boot the machine properly with JUST card 2 in slot 2?

Power is always a likely problem, but your PSU seems beefy enough AND you tested with a low-end card+GX2 (which also failed).

Which leaves BIOS. you may try even older BIOS revisions just to check if it was something the motherboard engineers broke recently. And clearly press them hard in email.


I updated the BIOS from 1300 to 2704 (the latest ASUS BIOS)

and find that the system is still not booting properly.

I will be trying the following things.

(1) Repeat the booting with a low power nvidia card

(2) Repeat the booting with a low power nvidia card and 9800gx2

(ensure that it is booting properly and the issue is not due to BIOS)

Maybe then upgrade to 1000 W PSU and try again.

I think the culprit is the PSU.

I am going to throw away the 850W Antec (not certified

in the SLI-ZONE for dual 9800gx2 configuration) and

replace with a corsair 1000w PSU (certified in

I made a mistake by just looking at the 9800gx2 power

supply website (

and the Antec specification (claiming dual graphics card SLI ready…)

It does not talk about dual 9800gx2 configuration. :angry:

Thanks all for the assistance.

Regds, Jay