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X399 Motherboards with Bifurcation support?

So in all my googling these past couple hours I cannot seem to find out which X399 motherboards support PCIe Bifurcation, can anybody recommend?

Also I’m not sure which has decent IOMMU groups for passing stuff through to VMs and whatnot as I’m likely going to start dabbling in that in the near future.

Boards I have to choose from at the moment are:

  • MSI X399 Carbon
  • Asrock X399 Taichi
  • Gigabyte X399 Gaming 7

Would love any help in choosing which motherboard I should go with or if another would suit me better.

Thanks!

Go ahead and vote if you want too! (fancy feature I haven’t tried yet:P)

  • MSI X399 Carbon
  • Asrock X399 Taichi
  • Gigabyte X399 Gaming 7
  • Other X399

0 voters

Asrock X370 and X470 ITX boards support Bifurcation. Not sure if that carrys through to the rest of their lineup.

Thanks!

From a bit more searching I found a post that claims it works on the Asrock boards so I’m definitely leaning towards one of those

Bit late to the party but I’d just like to mention that the Aorus Xtreme also supports it, if that’s any use.

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AsRock x399 Taichi and Professional Gaming both support Bifurcation on their 3rd PCIe x16 slot (last time I checked, may be allowed on top slot as well now)

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Last time I was in BIOS (recently updated to v3.30), all full length slots on the X399 Taichi support bifurcation.
Previous BIOS (v2.00), from memory, only supported the 3rd slot.

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I have the ASRock X399 Taichi and it has mostly great IOMMU groups. I dislike the following traits, but none of them is a dealbreaker to me:

  • Both onboard NICs are in the same IOMMU group (with a bunch of other stuff). I believe this is due to the X399 chipset, though.
  • The temperature source setting for fan control in the BIOS is not optimal. Only the very volatile Tdie or the slow / imprecise socket temperatures can be used. There really should be a time-averaged Tdie source.
  • More of a GPU problem than a motherboard problem: I have two 2-slot GPUs in the x16 slots, which only leaves me with the PCIe x1 slot. But this is attached to die 0, I would need it on die 1. This means that I will need a 1-slot GPU for the host.

I use 4x 8GB 3200 CL14 RAM and don’t have any stability issues whatsoever. I have heard of others who had to use lower clocks on motherboards of other manufacturers because they ran into issues.

Can’t say anything in regards to bifurcation.

Edit: Just saw that this thread is over a month old, whoops. Sorry about that, but maybe it will help someone else.

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No worries, The info is helpful :slight_smile:

I ended up getting the X399 Taichi board myself and when I checked the UEFI all slots supported PCIe bifurcation but only in the x4 variety (so an x16 slot can only be an x16 or an x4/x4/x4/x4)

Was hoping for and x8/x8 option :confused:

I’ve heard of some boards BIOS’s being modified to support it, anyone have any info in that regard?

Thanks for all the replies BTW!

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The Asus Zenith extreme x399 can support bifurcation accross all pcie and be x16→x8x8/x4x4x4x4/2x2x… Or the combinations of them to make x16 from reading their product page and bios reviews

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That is great to know, thanks for sharing!

if I don’t figure out a way to work around the x4/x4/x4/x4 limitation then I might pick one of those up :+1:

Hi, I’ve been looking for the bifurcation settings on a Gigabyte board…can you tell me where they are? I have an Aorus X399 Gaming (not Xtreme), but hopefully, they are in same place…Thanks!

Bit old thread, but since I have the Taichi, it seems appropriate. Would the ASUS HYPER M.2 x16 PCIe VROC RAID Card work on the Taichi? I do not need the raid, just 4x NVME ssd’s in one 16x slot, so I don’t waste the other slots

Yep, should work - there is an option in the BIOS to set the slot to x4/x4/x4/x4 instead of x16. No other options like x8/x8 as I had originally hoped tho :frowning:

OK, thanks. The fact it’s meant for Intel RAID will not stop it from working on AMD boards, but without Raid?

Has anyone had any luck bifurcation TWO x16 slots to x8x8 simultaneously? I have PCIE1 bifurcated to x8x8 and it seems to work fine…but I haven’t been able to get any other slots running bifurcated simultaneously (these are with GPUs). I can set PCIE3 to x8x8 and as long as one gpu is plugged into the splitter (AmeriRack), it posts fine and is recognized in Windows. As soon as a second card is connected, the system won’t post. I’ve tried the x8 slot at x4x4 as an alternative, but it runs into the same issue. Any architectural reasons you couldn’t have two slots bifurcated simultaneously?

So you have two GPU on a riser, or do you mean one GPU is on a riser and one plugged into the mainboard?

Can you share a picture of what you have put together?

Maybe power related?

Do you have Above 4G decoding enabled? might be needed with that many PCIe devices…

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Thanks for the tip, I’ll give that a try!

Correct, two GPUs on an AmeriRack x16 to x8x8 riser. In PCIE1 it works great and gets the system up to 5 gpus that run no problem (3 in the mainboard and 2 on a single x8x8 riser). As soon as I bifurcate a second slot and add a second gpu to the riser the system stops posting (oddly, a single gpu on the second x8x8 riser posts). Shouldn’t be a power issue, they’re on a 1500w PSU and I shouldn’t be anywhere near that draw at the moment (many of the gpus only draw 150w max).

You may need to enable above 4g decoding with multiple gpus

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Was just thinking, GPU don’t exclusively draw current from the external connector but also the bus. My thought is the riser might not be capable of providing enough current for two GPU, despite whatever it has for its own power connector.