What does "SLI ready" really mean?

We all know that "SLI ready" means that Nvidia have certified a motherboard as being suitable for supporting 2 or more graphics cards paired together to render frames cooperatively.

What do Nvidia look for in asserting that a motherboard is "SLI ready"?. Is it simply the existence of 2x suitably placed (physically) PCI-E slots and sufficient lanes to back them? (I.e. at least enough lanes for x16 and x8?)

Or is there more to this certification than simply validating that criteria is met and presumably paying a bit for a premium logo on your packaging? What exactly are the criteria that Nvidia will be looking for? Is there any thing technical, either physical layout, electrical or software/firmware that is either required or used to distinguish a certified vs no certified motherboard?

Flexo

Posted 2017-08-06T18:38:32.747

Reputation: 1 897

They likely have an engineer standards documentation. If that standard isn't published publicly this is very difficult question to answer – Ramhound – 2017-08-06T19:03:05.693

True, but not impossible to answer, e.g. by comparing seemingly similar certified (and working) motherboards with superficially comparable non-certified (and not working) motherboards it should be possible to identify any significant differences. – Flexo – 2017-08-06T19:10:25.487

AMD was actually earlier with their SLI. Its not an NVidia thing. Except that AMD calls it crossfire. – LPChip – 2017-08-06T19:38:57.060

The question could add "or crossfire ready" everywhere and still be as interesting. I think 3dfx were first to market in the consumer space (http://www.geekometry.com/2013/12/3dfx-voodoo2-the-original-sli/) but that's not really relevant and I never could afford a pair of Voodoo 2s.

– Flexo – 2017-08-06T19:45:57.140

Answers

When SLI and Crossfire first appeared, due to patent rights, motherboards could work with either SLI or CF. You had to use driver hacks that allows you to do SLI on CF board and the vice-versa. After everything was legally settled, now any MB supports both of them. So it was a legal matter, not a technical in nature one. Technically, it was the drivers that made everything possible, not the MB architecture. It is the video driver that dictates the way multiple PCI-E video cards communicate with each other.

Overmind

Posted 2017-08-06T18:38:32.747

Reputation: 8 562

I install the same video driver bundle regardless of the certification status of the motherboard. What does the driver bundle look for? Is it a built-in whitelist of information that's checked against e.g. dmi? – Flexo – 2017-08-07T07:01:21.703

The drivers detect your MB just like they detect your video card. – Overmind – 2017-08-07T10:50:35.057

Sure, but do they only care about chipset features that are actually needed for it to work, or do they maintain a whitelist and if it's the latter exactly which of the many identifiers a motherboard presents do they rely on? It's analogous to detecting user agents in JavaScript for a webbrowser or detecting the APIs needed for the script to work. – Flexo – 2017-08-07T16:59:39.497

It depends on the generation of chipsets. nV had very specific chipsets like nForce2 that may have used additional hardware tricks to prevent other than SLI from working. But as I said, it's ultimately up to the drivers. – Overmind – 2017-08-08T08:40:40.783

P.S. lanes have nothing to do with anything. – Overmind – 2017-08-08T09:21:42.283