Can B650 boards even support two GPUs (for passthrough)?

[tommy_goodshoes]

Most B650 boards have 3 PCIE slots with the following layout:
1x PCIe 4.0 x16, 2x PCIe 3.0 x16 (x1)

As an example, here is the Gigabyte B650 Gaming X AX.
The first slot is PCIe 4.0 x16, and the two bottom ones are PCIe x 3.0 x16 physically, but x1 electrically.

Question:

Can you add a GPU in the first X16 slot and a second one in those electrical x1 slots?
The first card being passed through and the second one used by the host.

[crispy_bacon]

I’ve never tried, so take it with a giant pile of salt.

In theory: Yes - but with bandwidth limitations.
In your use case, maybe the host GPU will be a wimpy low power one, which you might not care.

Now, the problem is that I don’t know if the BIOS supports it.
AFAIK “SLI supported” means x8x8 bifurcation, and “crossfire supported” meaning x16(CPU)x4(chipset) for GPUs, both supported and tested by the manufacturer. (Maybe I’m wrong, don’t quote on me)
Although since both of the technologies are basically obsolete, some start to not even bother with it, (e.g. TUF GAMING B650-PLUS WIFI) which is concerning.

I don’t know if the manufacturers have tested putting a GPU on those x1 slots, and if it properly works. (BIOS, driver, GPU firmware all might be not tested for x1 links)

TLDR:
It should work, but I haven’t tried. A safer bet (and a better performance one) would be to find a “crossfire” ready one, with x4 links.

[tommy_goodshoes]

Hey man, thanks for confirming my suspicions.

Normally, the rule of thumb has been that Nvidia cards require > x4 (electrically) to operate.
This rule was established during the good old PCIE 2.0 days, so I guess that could mean PCIE 3.0 x2 and possibly PCIE 4.0 x1 now?

I just can’t imagine board manufacturers completely removing the possibility to even operate two GPUs, despite that fact that SLI/Crossfire is officially dead.

So I guess like you said, it will come down to whether the board even posts with a card in the x16 and x1 slots.

Safest bet, again like you said, is to go for a board with an x16 and x4 slot, which is officially Crossfire ready labeled, but I still can’t help but wonder if it was actually possible with the x1.

There are also some boards who combine the 2x x1 slots like the B650 MSI Tomahawk. That one has a PCIE 4.0 x16 and PCIE 3.0 x2 slot. Chances might be slightly better that a second GPU could be supported in the x2 slot.

I’m getting a B650 board soon, so I guess I’ll try it out myself and report back.

Thanks for the reply!