Questions about SLI and running 3 GPUs at x16

CobaltImpurity · Dec 18, 2015

So my Dads laptop died and now he wants a desktop with three Titans, and three 4k monitors for playing EVE Online and doing some rendering for work (he's an electrical engineer so he uses autocad and such). I've already told him that it's overkill-and-a-half but he wants them anyway... and I thought I was power hungry. So, basically I'm here asking what motherboards out there will allow you to run 3 GPUs at full 3.0 x16 lanes.

And on that note, how does SLI actually work when it comes to lane speeds. When you look at the motherboard specifications and it tells you how many GPUs it can support and giving lanes speeds e.g. (x16/x8/x8 or x16/x16/x8, is this example for when you're using them in SLI or are they not related. Also if you could run down the difference between 40 lane and 28 lane that would be awesome.

Also, does the socket or chipset have anything to do with it? Because the plan is to give him a 6700k if he's gonna go this ham, and I'm not really up to date on the new chipsets and stuff.

Thanks guys, really appreciate it!

P.S. I already know someone is going to tell me to not get 3 titans or anything for him but I really just need answers to these questions, not a lecture on why he wouldn't need them, thanks!

timeconsumer · Dec 18, 2015

Short answer. None.

The PCI-E lanes are limited by the CPU and the chipset. The most you can get is x16/x16/x8 by using a Core i7 5960X or a 5930K.

The 5820K can support x8/x8/x8 on the proper board. This is probably the best option for him. Some boards will do x16/x8/x4 which wouldn't work.

So the board tells you what it theoretically can do given the proper number of lanes on the CPU. But you need the right CPU for it.

The 6700K can't use more than x8/x8 as 4 of its 20 lanes are across the DMI.

Wolfshadw · Dec 18, 2015

To my knowledge, there are no motherboards that will run three cards at 3.0 x16. I'm fairly certain they would run at 3.0 x8. I also believe the CPU determines the maximum number of PCIE lanes.

Found the following on the Intel ARK page for that processor:

PCI Express Revision 3.0
PCI Express Configurations ‡ Up to 1x16, 2x8, 1x8+2x4
Max # of PCI Express Lanes 16

-Wolf sends

faalin · Dec 18, 2015

The only way to get full 3x 16x lanes is to go with a x99 chipset socket 2011-v3 and a i7 5930k or 5960x Those are the only cpus that have 40 pci-e lanes on them.

The 6700k will only do two cards at 8x for sli or run 8x and 2@4x for 3 way crossfire.

timeconsumer · Dec 18, 2015

faalin :

16x3 = 48. Still not enough lanes even on 5930K or 5960X. Best he can do is 16/16/8

But honestly 8/8/8 on a 5820k will be just as good.

xxxlun4icexxx · Dec 18, 2015

CobaltImpurity :

Just a note on this if you are going to do a 3-way sli on an x99 board go ref fan or water. I made the mistake of tri-sli 980s on one of the largest boards (asus rampage) and had lots of cooling problems with non-ref fans, not to mention it's a dang tight fit.

Anyways, maybe a non-issue for you but I figured i'd put my .02 in. Good luck!

06yfz450ridr · Dec 21, 2015

are you talking about 3 titans or titan xs?

what programs does he exactly use? autocad doesn't really need a super gpu unless you are making some crazy stuff.

regular autocad barely uses any gpu power, they only use a single cpu core and some gpu.

other versions of autocad like maya etc will use more gpu. but not much

you might as well grab a single card or just dual cards and be done with it, I don't think any support sli in autocad atleast but he may use other programs that might

Sef Thomas · May 15, 2016

This is ridiculous. And NO., 3 4k monitors at high frame rate , that is NOT overkill.
That is needed for pushing so many pixels on 4k monitors.

However, it's the wrong direction on the CAD side.

AutoCad (Autodesk) and any high count 2D Wireframe CAD program really WANTS The Tesla, Quadro etc. Cards, if you want to push the VISUALIZATION in real-time of complex models. They are far more optimized for Billions of tiny elements, rather than Textured images at a high frame-rate. You Don't care about Framerate (<$1000 Gaming Cards) , or even about Bandwidth (SLI at x16 vs x8) much unless he is doing 3D simulation, or Feature quality Video production from 3D models. you don't want a Gaming hard, no matter how high end, for Electrical Engineering CAD.

Probably one of the highest end setups he could do at this point is 1 or 2 Huge Tesla Cards ($4000) and/or 1 or 2 Titan X or Z's, and that would cover about any kind of High-end cad AND GPU 3D rendering.

However, if he either doesn't do photo-realistic rendering, or doesn't use a GPU render program (Octane) but uses V-ray or 3Dmax instead, then FORGET the gaming cards and Pump up the CPU or even buy a Dual CPU board.

GAME cards are great for Framerate / 4K, BUT Engineers DONT NEED SLI!!! Multi-GPU rendering, like Octane Render ALSO doesnt' benefit from SLI.

On the other hand, if EVE online is now his job, then forget all the above, and get a 5960x, 3 Titans on a Great EVGA mobo, Great noctua cooling and call it a day.

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