Please recommend Ryzen ITX board with x8x4x4 bifurcation and good IOMMU groups

Per the title, I’d like an ITX board as already have NCase M1. Currently have 3900X but may upgrade to 5950x if the craziness ever dies down.

I’d prefer something passively cooled, but have heard the x570 chipset better for IOMMU. So not sure which.

Really want x8x4x4 as would allow a low profile card for Linux plus an extra SSD.

If I’m reading this right, you’re talking about dicing up 1x16, to 1x8 + 2x4s [3 peripherals]?

Part of me would want to say, playing it safer with investigating ATX boards, as the chipset will host an x4 slot (phys. x16), usually set at bottom of mainboard [leaving your CPU lane divvying from that 1x16 to 2x8s]

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ASRock X570 Phantom Gaming X [ATX] PCIe lanes example:
AMD Ryzen series CPUs (Vermeer, Matisse)

  • 2 x PCI Express 4.0 x16 Slots (single at x16 (PCIE1); dual at x8 (PCIE1) / x8 (PCIE3))*
    AMD Ryzen series CPUs (Renoir, Pinnacle Ridge)
  • 2 x PCI Express 3.0 x16 Slots (single at x16 (PCIE1); dual at x8 (PCIE1) / x8 (PCIE3))*
    AMD Ryzen series CPUs (Picasso)
  • 1 x PCI Express 3.0 x16 Slot (x8 (PCIE1))*
    AMD X570 Chipset
  • 1 x PCI Express 4.0 x16 Slot (x4 (PCIE5))*

ASRock X570 Phantom Gaming ITX PCIe lane example:
AMD Ryzen series CPUs (Vermeer, Matisse)

  • 1 x PCI Express 4.0 x16 Slot (PCIE1: x16 mode)*
    AMD Ryzen series CPUs (Renoir, Pinnacle Ridge)

  • 1 x PCI Express 3.0 x16 Slot (PCIE1: x16 mode)*
    AMD Ryzen series CPUs (Picasso)

  • 1 x PCI Express 3.0 x16 Slot (PCIE1: x8 mode)*

  • 1 x Vertical M.2 Socket (Key E) with the bundled WiFi-802.11ax PCIe WiFi module (on the rear I/O)

  • 15μ Gold Contact in VGA PCIe Slot (PCIE1)

*Supports PCIe riser cards to extend one x16 slot to two x8 slots if you install AMD Ryzen series CPUs
Supports NVMe SSD as boot disks

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I’d specifically like x8x4x4 to use with a bifurcator (that frustratingly I can’t link to). It allows one GPU x8, a low profile GPU at x4, and another nvme drive at x4

And I’d like ITX as it’s nice and small.

NVMe Boot, is tied to the CPU already. If you’re looking at accommodating dual M.2.s, do study all the upper ITX options. Some would only support 1 M.2 [being CPU], when others may support a 2nd slot, as Chipset support [whether its SATA, NVMe or accepting both signals]

You can have something like this, as your lane summary w/ the bifurcation:
CPU (20 Lanes) = NVMe(x4) + PCIe (x8) + PCIe(x8)
Chipset (4Lanes) = NVMe(x4)

Visual example of an ITX board, hosting 2 M.2 slots
https://www.newegg.com/gigabyte-x570-i-aorus-pro-wifi/p/N82E16813145159?&quicklink=true

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Might look into the asrock rack X570D4I-2T

There are a couple threads on here about it and its mATX brother. I’m pretty sure it has bifurcation, might ask them if it will do x8/x4/x4.

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