8800GTS in secondary 16x PCI-E slot

[RaphaF]

Hello,

I have recently acquired a nVidia 8800GTS, and my motherboard is an Asus A8N-SLI Deluxe running an Athlon X2 4400+. Because I'm using a passive cooler on my motherboard chipset, there isn't enough room to fit the 8800GTS in the primary 16x PCI-E slot, so I have to use the secondary 16x PCI-E slot.

Initially, I observed very poor performance (e.g. 3900 in 3DMark06) but I quickly realized that, by default, the secondary PCI-E slot only uses one lane. Then I activated the dual-video mode by switching the selector on the motherboard, which gives 8 lanes to each PCI-E slot. Performance increased dramatically e.g. 7800 in 3DMark06.

Now I'm wondering... Is 8x PCI-E sufficient to guarantee maximum performance with a 8800GTS? I've extensively Googled this topic, but I haven't found a satisfying answer. I know there're issues with the 8800 serie in *actual* 8x PCI-E slots, but here we're talking about a 16x slot set to 8x.

I tend to think that 8x should be fine, as the PCI-E interface was designed to provide enough bandwidth for future generations of videocards, and I believe that AGP 8x was never a bottleneck. Also, my scores seem in line with similar configurations' scores.

What do you guys think? Thanks in advance.

 

[Stumps]

It shouldn't make a difference at PCI-E 8x

 

[lopri]

2~3% performance loss at maximum. It depends on how the board/chipset configures PCI-E switches, rather than the theoretical bandwidth loss itself.

 

[Effect]

Hmm, i remember reading a review on the ASUS P5N-E SLI (nForce 650i) where they ran 2 8800GTX's in SLI (both running 8x PCIe) and had a 0% performance loss (compared to 8800GTX SLI on the 680i). So in short (if this review is to be believed), no....you shouldn't see any performance loss using the 8800GTS on 8x PCIe.

 

[lopri]

He isn't running SLI. There is a tiny (I mean, real tiny) performance drop using 2nd PEG instead of 1st PEG, but I believe it's not because of reduced of bandwidth. Rather, it's the way a board employ PCI-E switch and the distance between the CPU/NB and the GPU (hence latency).

 

[RaphaF]

Thanks guys. I had already observed that my system's performance was fine (in 3DMark, Oblivion and NWN2) compared to similar systems, but I don't know whether those applications are good benchmarks from a PCI-E performance perspective. Now I can sleep better at night, as 2-3% isn't important to me. Performance was definitely horrendous at 1x PCI-E though.

 

[Kromis]

Theoretically, you can sleep better at night.