SLI - 8x 8x working but not 16x 4x

[Maximus_Sa]

Hey everyone

Ive just got myself another 460GTX 1GB hawk edition, and have set up everything like one normally would for SLI.

In 8x 8x configuration (the top two slots), SLI works fine. However, my top card hits 85 - 90 within 10 minutes of gaming (there is about 0.5cm between the cards), but as soon as I switch to the 16x 4x configuration (slot 1 and 3), the Nvidia control panel does not pick up SLI. (shown on the right hand side of the pic below)

I have updated to the latest BIOS, got the latest drivers from Nvidia and the cards are exactly the same. (all other details are in the link below)

If someone could give me any ideas as to what may be causing this, it would be greatly appreciated.
Im really not looking forward to returning this mobo to Asus :/

Thanks in advance!

Specs: http://i.imgur.com/zSOhP.jpg

 

[johnnychuttz]

What mobo? Some don't allow SLI in the 3rd slot. Mine doesn't, its only x1.

 

[k1114]

Sli does not support 16/4, it must be at least 8/8.

 

[Wolfshadw]

My guess would be that there is nothing wrong with your motherboard. You're supposed to run SLI using the top two PCI-Ex16 slots in an x8/x8 configuration. As your manual states (pg 1-23):

Connect a Chassis fan to the motherboard connector labeled CHA_FAN1 or CHA_FAN2 when using multiple graphics cards for better thermal environment

-Wolf sends

 

[Maximus_Sa]

johnnychuttz - my motherboard is an p8p67 m-pro. It supports both Crossfire and SLI in any 3 (or all 3) of my PCI slots. My bottom slot is x4, hence it can run in SLI mode. For all other specs check the link in my first post.

k1114 - SLI does work on 16/4. There is a slight performance hit, but there are many reviews of 16x/4x SLI configurations.
For example: http://www.overclock.net/t/819348/16x-16x-vs-16x-4x-gtx-470-sli-comparison.
My motherboard manual also states it can run in 16x 4x mode.

Wolfshadw - I include a picture from my motherboard manual.
http://i.imgur.com/JAAsP.png
It specifies lane 3 and lane 1 can be used as SLI. (in 16x 4x mode)

Any other thoughts perhaps? :/

 

[Maximus_Sa]

I found an accurate answer - consider this thread closed: (a quote from another forum)

What I'm saying is you can run SLI in the two top slots, but not SLI in slot one and slot 3. Sandy Bridge wasn't designed that way. I read the manual as well and I believe its incorrect - ASUS support is, AFAIK, likewise not giving you the right information.

When Intel launched Sandy Bridge, many reviewers were concerned that it just didn't have enough resources to support multiple graphics cards. There are 16 native PCI-Express 2.0 lanes to the CPU as well as an extra four that could be used for anything else. Sandy Bridge-E and the Nehalem-based Core i7 chips have anything from 32-40 PCI-E lanes available for use, which is why any site that does graphics card reviews uses a LGA2011 board and compatible CPU for their multi-card configs.

Ivy Bridge is also limited to 16 lanes, but this time they are of the PCI-Express 3.0 variety. Its entirely possible to design a Z77-based board with four slots running at 4x each, with the same bandwidth and speed/throughput as PCI-E 2.0 8x. There's just the slight problem that many manufacturers don't do this, sadly.

 

[Mousemonkey]

I found an accurate answer - consider this thread closed: (a quote from another forum)

What I'm saying is you can run SLI in the two top slots, but not SLI in slot one and slot 3. Sandy Bridge wasn't designed that way. I read the manual as well and I believe its incorrect - ASUS support is, AFAIK, likewise not giving you the right information.

When Intel launched Sandy Bridge, many reviewers were concerned that it just didn't have enough resources to support multiple graphics cards. There are 16 native PCI-Express 2.0 lanes to the CPU as well as an extra four that could be used for anything else. Sandy Bridge-E and the Nehalem-based Core i7 chips have anything from 32-40 PCI-E lanes available for use, which is why any site that does graphics card reviews uses a LGA2011 board and compatible CPU for their multi-card configs.

Ivy Bridge is also limited to 16 lanes, but this time they are of the PCI-Express 3.0 variety. Its entirely possible to design a Z77-based board with four slots running at 4x each, with the same bandwidth and speed/throughput as PCI-E 2.0 8x. There's just the slight problem that many manufacturers don't do this, sadly.

So k1114 was correct then.

 

[Mousemonkey]

Best answer selected by Mousemonkey.

 

[Mousemonkey]

This topic has been closed by Mousemonkey