Two RTX 3090 GPU's in a Single Machine

The world is really against this idea these days...

I decided to take advantage of Prime Day and set up a proper 4-slot spaced dual RTX 3090 system, and man, what a pain. I've already got two of them crammed into a mid-size case with a 3-slot spread, and while that does indeed work at the end of the day, the cooling requirments are not a bit less than exessive. I happen to have 64GB of DDR5 RAM doing nothing, so I figure, let's shop on Prime Day for once and build up a non comprimised dual 3090 system on top of that.

With SLI for gaming dead for some time, there is no part of this build process looking to help you out with a 4-slot spaced dual 3090 set up with NVLink. Who would want such a thing? Most of the advice remaining, what little that is, is to vertical mount the cards and use PCIe risers, which is no good for the rigid NVLink connectors and their exacting spacing requirments between the two cards.

The first step is to find a motherboard with 4-slot PCIe spacing, with both slots connected to the CPU at 16x/16x or 8x/8x. This slot spacing is not advertised or mentioned in reviews, so you are basically eyeballing it off marketing pics or trying to find the few outdated mentions of what motherboards might cut it. Then the easy contenders are like $1-1.2k. No thanks.

With only a couple of hours left on Prime Day, I ended up settling for the Asus Maximus Hero. Spending so much time looking at so many boards, I had forgotten that I’d already eliminated it as not 4-slot spaced. But I saw the Asus Hero mentioned a few times as a 4-slot board, I had thought, and with the clock winding down, me a little tired, and it looking reasonable with some lazy eyeballing, I went with it, having forgotten I'd already rejected it.

When the board showed up with everything else, I opened it and could immediately tell it was not a 4-slot spaced board. Damn. I packed it up for return. It’s the Maximus Dark Hero that’s 4-slot, and the 790 Maximus Dark Hero still wouldn’t be released until the next week, come to find out. Reading the reviews for it now tells you a lot about what this slot spacing currently means to people. They all say the Dark Hero is identical to the Hero, except for the dark paint job, WiFi 7, and one other thing I don’t recall. Well, the slot spacing is different, too, buddy. And you call yourself a professional.

So I started searching again, and man, there is not a lot to find—extremely little when you rule out 1K boards. The $400-700 boards are already not at all considered cheap - 1.2K for the Godlike board is a bridge too far. I'm not even interested in overclocking anything, so all the extras don't do me much at all.

I finally found my board in the EVGA 790 Classified. It even came with a built in 10GB NIC, something I really wanted, considering 3 PCIe slots are viewed as a lot on these boards, and invariably, you will lose one under these monster graphics cards. Not even all the $1k range boards give you the 10GB. Score.

So I wait for it to come, and when it arrives, I start to set things up in the large, spacious, full-tower EATX case I’d paired it with. Oh boy, I had begun to worry about this ahead of time: even in such a large case, the PSU section at the bottom leaves just too little room to fit a 2.5-slot card in the boards bottom slot. Man.

Back to case searching. Again, there are not a boatload of options. A decent chunk of possibilities are sold out. I look at alternatives. You can shrink the size of the card with water cooling. But I’m not interested in building a custom loop. I see like one possible AIO cooler that will work with this card, but reviews are not great, and it doesn’t ship for some time.

They stopped making the two-slot blower style 3090s, but I took a look on eBay thinking, maybe I’ll just add another card. Rather than $700-800 used, these guys go for like $1500. That's $100 short of an RTX 4090, which can often be equivelant to almost two 3090's outside of having half the VRAM.

Back to cases. Finally, after plenty of time, I find one that is decent and doesn’t have the power supply in the bottom back of the case, under the cards, and that ships sometime this year. Fingers crossed. If this doen't get me there, I'm pulling out the dremel.