You might look for an HP Z800 (dual skt 1366) motherboard. Has at least 2 GPU slots 3 spaces apart. I ran one here for a long time with 2 dual slot cards. WARNING: motherboard plugs are proprietary and require an adapter to use a standard power supply (available on ebay for ~ $10). OR: you could find a complete Z800 workstation relatively cheap on eBay. (You only need a near-bare bones one, not a fully loaded one, which can be costly). Make sure you get the MB variant that can use dual Xeon X56nn CPUs.

Takes DDR3 server RAM, which is quite cheap on eBay these days.

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You might look for an HP Z800 (dual skt 1366) motherboard. Has at least 2 GPU slots 3 spaces apart. I ran one here for a long time with 2 dual slot cards. WARNING: motherboard plugs are proprietary and require an adapter to use a standard power supply (available on ebay for ~ $10). OR: you could find a complete Z800 workstation relatively cheap on eBay. (You only need a near-bare bones one, not a fully loaded one, which can be costly). Make sure you get the MB variant that can use dual Xeon X56nn CPUs.

Takes DDR3 server RAM, which is quite cheap on eBay these days.

It also runs pretty hot so you may need to use TThortle on it to keep it from over heating.

I actually have a Z400 running two double wide gtx 750Ti's for sale :) But it isn't a two cpu system. Only runs 6c/12t.

You may be able to find used Intel 2 cpu MB's. They run e5-2670 type cpus. And the one I had before it burned out, had space for 2 maybe 3 double wide gpus.

I have this MB: ASRock EP2C602, it will run 3 gpus, I think, and certainly could run 2 far from each other. I think the pretty cheap X79 Generic MB's on eBay will too. Warning, those don't run turbo-mode at all.

HTH,
Tom

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A proud member of the OFA (Old Farts Association).

Yep, I have the Asrock EP2C602 also, and for awhile, I ran 3 x gtx980s on it. They were the blower-style cards, and didn't mind being near each other as much as the open style would.

Something like the Rampage IV Extreme (single-cpu X79) has 7 physical PCIex16 slots, and using 1, 4 and 7, you could run 3 GPUs with some space between them.

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It also runs pretty hot so you may need to use TThortle on it to keep it from over heating.

Once again the program is called TThrottle as in Throttle not Thortle

Look at this link

http://andybrown.me.uk/2014/11/01/z800/

for all the gory detail about using the Z800 motherboard, and this one

http://www.andybrown.me.uk/forum/index.php/topic,14.0.html

for extensive discussions about it.

Even if you don't wind up doing it, it's a fun read for the ingenuity shown and the doggedness of the pursuit.

Just make sure you get the -003 version of the board. (AS# 460838-003 on the label) - see 2nd pic in the first link

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An Intel S5520HC may be worth looking at, they can be found quite cheap with up to 96Gb. I have one that came with 2xE5630 and 12Gb RAM, upgraded it to X5680. I was quite impressed with the E5630s originally in it for the $200 CAD it cost me. It's my NAS box so I don't push it too hard with big cards (1050/750Ti). It was a bit of a pain with the CPU coolers (2 x MasterCooler D92) since the 'pads' aren't standard - I used VGA/Serial I/O shield standoffs and some scavenged M3 screws.

EDIT1: And I took a Dremel to the other two PCIe slots to allow for a 16x card.
EDIT2: It has no sound BTW.
EDIT3: It is a BIG board SSI/CEB I believe, so a bigger case is needed.

A $110 USD example: Intel S5520HC S5520HCR, LGA 1366,with 2 x Xeon L5640, 12GB

It also runs pretty hot so you may need to use TThortle on it to keep it from over heating.

Once again the program is called TThrottle as in Throttle not Thortle

I don't disagree. I just seem to have trouble with the spelling for some reason.

:(

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A proud member of the OFA (Old Farts Association).

The other thing you may notice is that if you want to upgrade your PSU you either go with HP or you create a custom adaptor. Standard PSU have one connector wire in the "wrong" place and the system won't boot.

Tom

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A proud member of the OFA (Old Farts Association).

HP has 2 different power supplies for these.
The larger power supply comes with more gpu plugs. It is 1050 watts, with all the proper proprietary connectors as your current 850 watt (I think) psu has.

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I have 2 HP computers, a desktop and a laptop, one with Windows 10 and another with SuSE Linux Leap 15.0, which has the same kernel of the Enterprise version. Both work well, one from 2012 (the laptop) and one from 2014 (the desktop). Both have AMD CPUs, the laptop an E-450 and an A10-6700 the desktop, which has also a GTX 1050 Ti GPU. Both work 24/7 also in summer, no AC. I have also an ENVY 4500 printer, connected via WiFi to the router. I have enlisted in a HP Print Connect program, which gives me HP cartridges when mine become empty.
Tullio

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So how is it running? Your computers are hidden so I can't look :)

Tom

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A proud member of the OFA (Old Farts Association).