Performance loss with PCIe 4x vs 16x?

[WobbleWobble]

I just bought a 7900GTO and this thing is huge. I have an Asus A8N-E with a Zalman northbridge heatsink that blocks the installation of the GTO in the 16x slot. I am able to fit it in the 4x slot and things seem to be working fine. I doubt that a 7900GTO can saturate even a PCIe 4x slot, so I think I'm fine but I haven't found any benchmarks to back my thoughts up. Afterall, AGP 4x/8x showed virtually no difference.

Your thoughts?

 

[F1shF4t]

Well a pcie 4* will roughly equal agp 4* (well not really as pcie has the same transfer speed both ways)

So i would think that it would start to saturate the slot, i guess u will loose some performance but i doubt it will be much.

 

[hans007]

i had an a8n-e before.

that x4 slot is only physically x4. it is electrically an x2 slot. so yeah you probably are losing some performance. i believe x2 pci-e is about the equivalent of agp 2x.

 

[BlingBlingArsch]

id say give it a try, but i agree with Cupcake, there should be a significant performance loss in certain games and with certain resolutions & AA/AF settings.


PS: rather large dl but this bench is very sensitiv to changes in bandwith http://www.spec.org/gpc/opc.static/prev_benchmarks.html

 

[Lonyo]

With 8x/8x vs 16x/16x in SLI there is a difference in performance, only slight in most cases, but I would guess 4x would have a noticeable difference to 16x with a single card.

 

[Dman877]

Buy a new NB heatsink or mod the one you have so the card fits in the 16 slot. Is it a finned or pinned heatsink? If so, just bend them out of the way.

 

[n7]

Actually, according to AT (see the P5B-D Crossfire review), there is minimal loss in using a 4x PCI-e slot.

And i'd tend to believe that.

Someday when i get time i'm gonna test my X1900XT in my 4x slot to see how it compares to the 16x slot.

 

[beemercer]

It'll be alright temporarily, but definitately get another solution.

 

[Madellga]

Originally posted by: n7
Actually, according to AT (see the P5B-D Crossfire review), there is minimal loss in using a 4x PCI-e slot.

And i'd tend to believe that.

Someday when i get time i'm gonna test my X1900XT in my 4x slot to see how it compares to the 16x slot.

That in Xfire mode - which doesn't double performance anyway. I think the impact on a single card would be more noticeable.

 

[Canterwood]

Originally posted by: hans007
i had an a8n-e before.

that x4 slot is only physically x4. it is electrically an x2 slot. so yeah you probably are losing some performance. i believe x2 pci-e is about the equivalent of agp 2x.

This is correct.

I have an A8N5X, which is basically the same board.
The PCI-E x4 slot only runs at x2 speed, so there would be a performance hit.

Try to get a low profile heatsink for the board so you can use the x16 slot.

 

[WobbleWobble]

Any passive heatsink that sits on top of the chip would be too big. I am NOT going back to the little whiny fan (silence > performance). I like the GTO cooler, so I'd rather not spend money to replace it. That leaves replacing the northbridge heatsink with a SLI friendly one, something like the ThermalRight HR-05 SLI and the Jing Ting cooler. Availability of the Jing Ting cooler is non-existant in Canada and I'm waiting for a specific store to stock the HR-05 SLI since they are significantly cheaper than many other stores. Hopefully they'll fit as well.

Bending the Zalman right now doesn't look feasible as I'd have to bend more than half the fins.

 

[bcoupland]

I was in the exact same predicament as you. I have the A8N-E and the NB47J. I ordered the 7900GTO with an HR-05 SLi from NCIX on friday. Unfortunately, the HR-05 will take a little while longer because it wasn't in stock but i'll just put it in the bottom slot for now. I think that you can disable the other pci-e 1x slots with a jumper or in the bios to run the 4x slot at 4x speed.

 

[WobbleWobble]

Originally posted by: bcoupland
I was in the exact same predicament as you. I have the A8N-E and the NB47J. I ordered the 7900GTO with an HR-05 SLi from NCIX on friday. Unfortunately, the HR-05 will take a little while longer because it wasn't in stock but i'll just put it in the bottom slot for now. I think that you can disable the other pci-e 1x slots with a jumper or in the bios to run the 4x slot at 4x speed.

I've put back on my original chipset fan and will benchmark to see if there is a performance difference between the 16x slot and the 4x slot. I will also look to see if I can enable 4x mode for the 4x slot.

I got my hands on the Jing Ting chipset cooler to see if it would fit. The Jing Ting doesn't off set it self enough to be mounted horizontally, so it would only fit vertically which isn't the ideal situation. The Thermalright HR-05-SLI would probably have the same problem. It

P.S. I can't believe how loud the original chipset fan is... it started driving me crazy!

 

[LLoose]

http://forums.anandtech.com/messageview...atid=31&threadid=1945538&enterthread=y

This guy is a prime example of what happens when you are running 4x..

 

[WobbleWobble]

I benched my stock 7900GTO on my Opteron 165 @ 2.4GHz with 3DMark06.

PCIe 16x - 5732 marks
PCIe 4x - 4488 marks (or 2x if that's true)

I can't find a way to enable 4x in that slot in the BIOS or via jumpers on my board. Not that I don't believe you guys, but I can't find any info that the 4x slot is really a 2x slot. Perhaps you guys can point to a link for me please?

Regardless, there is a signifcant performance hit so I've ordered the Thermalright HR-05-SLI.

 

[Canterwood]

Originally posted by: WobbleWobble
I can't find a way to enable 4x in that slot in the BIOS or via jumpers on my board. Not that I don't believe you guys, but I can't find any info that the 4x slot is really a 2x slot. Perhaps you guys can point to a link for me please?

I used CPU-Z, which listed the slot as running in x2 mode when I put a video card in there.