Let's dispel two Windows GPU mining myths..

[Meatball]

Hmm, that's awesome.  Of course, you run into power requirement issues with that many cards, but it's nice to be able to bundle things up into fewer machines.

So, that leads to the question of what are some good suggestions for motherboards that have 5+ PCI express slots?

I'm running an ASUS WS Revolution with 7 GPUs with Windows 7, AMD currently has a ticket from me escalated to engineer to deal with the need for dummy plugs with 11.6.

Nice.  What GPU's/PSU are you using?  My main concern with 5+ cards isn't really the overall power needs of the cards, it's that I believe the cards can draw 75W through the PCI express slots.  7-8 cards is 600 watts pumping through the board just for the GPU's and I wonder if that would be any cause for concern?

[NANO]

Guys please help me here! I cant get to work with 3 cards (5 GPU) and this is my four day with the problem and still no solution

http://forum.bitcoin.org/index.php?topic=21687.0

[dishwara]

I tried to mine with 8 GPU's in Linux - Ubuntu 11.04. Mother board is MSI big bang Marshal. The problem is not Linux but PSU.
I can mine with 8 cards , if don't over clock, don't have any fans installed....
To cool GPU's i use 120 mm fans, 6- 8 fans & PSU can't able to give power with 8 cards + fans.
I used 2 PSU's & i still can't believe the PSU sucked.
Cooler Master Silent Pro Gold 1200 W. Before buying i wrote to cooler master & got confirmation that it will support 8 GPU's.
Yes it supports 8 GPU's in Ubuntu, but mining & adding fans makes the PSU to go off.
Then i used another PSU, 3, 1200 W to mine with 8 cards, but due to not able to under clock memory of 6970's heat went up to 95C+ , so stopped using that.
My advice, unless you know how to cool, avoid more than 6 GPU's.
Also Cooler Master even though having 80 gold certificate sucks, seems they got fraud certificate or something & also in AMD's certified PSU's only 2 nos of 5870 is mentioned as CMSPG 1200w supports.

If you want more power, yesterday found out, silverstone ST-1500W can able to with stand 4 GPU's , I emailed them & they confirmed.
Still cooler master gave me failure , i can't trust it now. But 1500W can support, i hope.
My system had 5 nos. of 5870's (2 ASUS EAH 5870, 1 Sapphire HD 5870, 2 MSI R5870 Lightning) & 3 nos. of MSI R6970 Lightning.

[Parja]

Well, I know for a fact Windows XP doesn't have a hard 4 GPU limit.  I used to run Folding@Home on 4 9800GX2 video cards, so 8 GPUs, on Windows XP x64.  If there is an issue, it's manufacturer specific then.

I tried to mine with 8 GPU's in Linux - Ubuntu 11.04. Mother board is MSI big bang Marshal. The problem is not Linux but PSU.
I can mine with 8 cards , if don't over clock, don't have any fans installed....
To cool GPU's i use 120 mm fans, 6- 8 fans & PSU can't able to give power with 8 cards + fans.
I used 2 PSU's & i still can't believe the PSU sucked.
Cooler Master Silent Pro Gold 1200 W. Before buying i wrote to cooler master & got confirmation that it will support 8 GPU's.
Yes it supports 8 GPU's in Ubuntu, but mining & adding fans makes the PSU to go off.
Then i used another PSU, 3, 1200 W to mine with 8 cards, but due to not able to under clock memory of 6970's heat went up to 95C+ , so stopped using that.
My advice, unless you know how to cool, avoid more than 6 GPU's.
Also Cooler Master even though having 80 gold certificate sucks, seems they got fraud certificate or something & also in AMD's certified PSU's only 2 nos of 5870 is mentioned as CMSPG 1200w supports.

If you want more power, yesterday found out, silverstone ST-1500W can able to with stand 4 GPU's , I emailed them & they confirmed.
Still cooler master gave me failure , i can't trust it now. But 1500W can support, i hope.
My system had 5 nos. of 5870's (2 ASUS EAH 5870, 1 Sapphire HD 5870, 2 MSI R5870 Lightning) & 3 nos. of MSI R6970 Lightning.

Well duh, of course a single 1200W power supply isn't going to be able to handle the load of 8 GPUs.  You get a max of 98A @ 12V, so 1176W to work with on the 12V line.  Figure your system probably has around 100W overhead, so you're down to 1076W to split among 8 video cards, or 134W each.  Unless you're using some pretty low performance video cards, you're overloading the power supply.  You're probably going to have to run a second power supply to power at least a couple of those cards.

[dishwara]

I tried to mine with 8 GPU's in Linux - Ubuntu 11.04. Mother board is MSI big bang Marshal. The problem is not Linux but PSU.
I can mine with 8 cards , if don't over clock, don't have any fans installed....
To cool GPU's i use 120 mm fans, 6- 8 fans & PSU can't able to give power with 8 cards + fans.
I used 2 PSU's & i still can't believe the PSU sucked.
Cooler Master Silent Pro Gold 1200 W. Before buying i wrote to cooler master & got confirmation that it will support 8 GPU's.
Yes it supports 8 GPU's in Ubuntu, but mining & adding fans makes the PSU to go off.
Then i used another PSU, 3, 1200 W to mine with 8 cards, but due to not able to under clock memory of 6970's heat went up to 95C+ , so stopped using that.
My advice, unless you know how to cool, avoid more than 6 GPU's.
Also Cooler Master even though having 80 gold certificate sucks, seems they got fraud certificate or something & also in AMD's certified PSU's only 2 nos of 5870 is mentioned as CMSPG 1200w supports.

If you want more power, yesterday found out, silverstone ST-1500W can able to with stand 4 GPU's , I emailed them & they confirmed.
Still cooler master gave me failure , i can't trust it now. But 1500W can support, i hope.
My system had 5 nos. of 5870's (2 ASUS EAH 5870, 1 Sapphire HD 5870, 2 MSI R5870 Lightning) & 3 nos. of MSI R6970 Lightning.

Well duh, of course a single 1200W power supply isn't going to be able to handle the load of 8 GPUs.  You get a max of 98A @ 12V, so 1176W to work with on the 12V line.  Figure your system probably has around 100W overhead, so you're down to 1076W to split among 8 video cards, or 134W each.  Unless you're using some pretty low performance video cards, you're overloading the power supply.  You're probably going to have to run a second power supply to power at least a couple of those cards.

Before answering, READ what said.

[chungenhung]

I tried to mine with 8 GPU's in Linux - Ubuntu 11.04. Mother board is MSI big bang Marshal. The problem is not Linux but PSU.
I can mine with 8 cards , if don't over clock, don't have any fans installed....
To cool GPU's i use 120 mm fans, 6- 8 fans & PSU can't able to give power with 8 cards + fans.
I used 2 PSU's & i still can't believe the PSU sucked.
Cooler Master Silent Pro Gold 1200 W. Before buying i wrote to cooler master & got confirmation that it will support 8 GPU's.
Yes it supports 8 GPU's in Ubuntu, but mining & adding fans makes the PSU to go off.
Then i used another PSU, 3, 1200 W to mine with 8 cards, but due to not able to under clock memory of 6970's heat went up to 95C+ , so stopped using that.
My advice, unless you know how to cool, avoid more than 6 GPU's.
Also Cooler Master even though having 80 gold certificate sucks, seems they got fraud certificate or something & also in AMD's certified PSU's only 2 nos of 5870 is mentioned as CMSPG 1200w supports.

If you want more power, yesterday found out, silverstone ST-1500W can able to with stand 4 GPU's , I emailed them & they confirmed.
Still cooler master gave me failure , i can't trust it now. But 1500W can support, i hope.
My system had 5 nos. of 5870's (2 ASUS EAH 5870, 1 Sapphire HD 5870, 2 MSI R5870 Lightning) & 3 nos. of MSI R6970 Lightning.

Well duh, of course a single 1200W power supply isn't going to be able to handle the load of 8 GPUs.  You get a max of 98A @ 12V, so 1176W to work with on the 12V line.  Figure your system probably has around 100W overhead, so you're down to 1076W to split among 8 video cards, or 134W each.  Unless you're using some pretty low performance video cards, you're overloading the power supply.  You're probably going to have to run a second power supply to power at least a couple of those cards.

Before answering, READ what said.

He used up to 3 power supplies, not one.