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I recall hearing that windows has a GPU limit that prevents running 3x6990's because that would 6 GPU's total. What is the windows limit and is it possible to run 3x6990 on Linux?

I don't think anyone has found any 'official' document on this, but it appears Windows is limited to 4 GPU's.  Linux can handle up to 8.

I'm still waiting for even unofficial evidence of this. So far it's been nothing but hearsay.

The only evidence I've seen thus far is people having trouble physically getting 5 video cards (not gpus) into place. But 4 double-gpus seems to be ok (meaning 8 gpus). Still waiting on some evidence either way.

The company building my 3x6990 system says windows isn't recognizing the 3rd card. I told them to test again with Linux, we'll see how that goes.

How did they convince you to buy those cards? Not trying to be a downer, but they are overpriced for what you get.

They didn't convince me. I'm confident that, for my purposes, this is the best system.

that sounds about right.  6990 is 2x GPUs

They only test with Windows so they're going to ship it today. When it gets here tomorrow I'll check it on Linux and see how that goes, then report back.

Try with windows first, so I can finally get some first hand data ;)

I'm almost at the point of buying a PCI-E extender cable so I can find out for myself... but not quite.

Just an update, my system wouldn't boot any OS at all with 3 cards in. I tried a windows install CD, ubuntu 11.04 install cd and install USB, then a hard drive with ubuntu 11.04 already installed.

Removing one of the 6990's allowed it to boot. This is frustrating, hopefully I can just stick this card in my old system.

For mining? 6990 is one of the best for price to performance. The difficult part is finding one, as it is sold out almost everywhere.

I wouldn't say they are the best "bang for your buck" card. They are 730$ each for 830 MH/s; but you could get 3 5850's for 450 (3*150), they each hash @ 300MH/s, totaling out to 900MH/s....

we really need a clear answer of this question. Hopefully some one can get it tested real soon.

are you using 64 bit OS? if not you might be ruining out of address space. and you can get 2 6950 for under $600 flash them and have the same mhs, the only time i see 6990 being good is if your out of pice slots

true, but you can do 2 x 6990 on the same rig, or even 3x. Then the $/Mh becomes much more favorable.

I fail to see how a single core 6950 would reach the same mh/s as a dual core 6990 even if you fool the 6950 into thinking it's a 6990

I did test it, the system wouldn't boot any OS with 3 cards (and thus 6 GPUs) installed. I only tested x86 OS's, however.

try a 64bit os and will it even post as in you can get to boises and stuff? you might be running out of bios address space try to disable every thing you don't need might just give you enough free space to boot

They are actually the opposite of this statement. A $700 dollar card (usually more) that puts out 800MHash/sec (often less) is $1.14 / MHash. A 5830 is about $2.85 / MHash.

Even factoring in stuffing 8 GPUs onto a single motherboard usually doesn't even out the cost ratio.

It posts but fails to load the OS and goes into a reboot loop.

super6

What is your PSU , acording to AMD for  2x6900   1000W shhould be at least  , 1200W  recommended .

Don't care how efficient the 6990 is !

There is no answer to "Windows GPU limit ?" in this thread yet,,,


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Edit: Here is our answer,,, : http://forum.bitcoin.org/index.php?topic=17949.0

I can confirm testing 8 GPUs (4 6990s) on Win7 64-bit without an issue using 11.6 drivers.  The issue you WILL have is insane heat with 6990s.

Almost have that solved with 450 CFM fan panel. :)

Was the motherboard's delivered power as issue ?

Note : I'm going for 5 using extenders on an old ep43-ds3l :)

You might be OK with extenders since the power is not drawn from mobo.  You'll have to test... You might have issues though with an older board.

I tested using 890FXA-GD70