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PCIe Lanes on Asrock X370 Professional Gaming and X470 Taichi Ultimate


While looking around I found some interesting spec “inconsistencies”. X370 and X470 have 8x PCIe 2.0, 4 SATA Ports and 2 SATA Express that each can be configured as 2x SATA or 2x PCIe 3.0.
After reading the manuals and looking at general x370/x470 block diagrams (I cant find them for asrock boards), this is how I think its layed out:
The X370 Professional has both SATA Express configured for SATA and the Taichi Ultimate one of them for PCIe to connect its 10GBit/s LAN. That leaves:

  • 4 lanes for the 3rd pcie / 2nd m2 slot,
  • 2 for the x1 slots,
  • 1 for I211 Lan
  • 1 for the wifi card
  • 1 for the ASM1061 SATA controller
  • 2 for the 5 Gbit LAN on the X370 Board / for the backpanel USB 3.1 on the Ultimate

Thats 11 Lanes for 8 available.
What am I missing?

Further thoughs:
ASUS downgrades the 4x slot to 2x when the x1 slots are used. This is not the case here, I have the X370 Taichi (Same board as the Professional Gaming minus 5 GBit Lan) and I’m using a 10 Gbit card in the lower slot and a SATA controller in the upper 1x slot. Each of the cards show no sign of throttling. Additionally a friend of mine has the Professional Gaming in his build. He uses a 2nd 970 evo in the 2nd m2 slot while using the 5Gbit controller and a sound card in the upper 1x slot. No signs of throttling either (Not counting PCIe 2.0 limiting the 970 evo to about 1.8GB/s).
I physically can’t find any PCIe switches or similar things on any of the boards (This time not counting the 4 that split 16x/0x to 8x/8x on slot 1 and 2). lspci shows nothing suspicious either.
Any Ideas?

Edits: Getting my facts straight :see_no_evil:

Edit2: Solved it!
lspci -tv shows wifi, lan and the two pcie x1 slots grouped together. Another check of lspci reveals the trick: PCI bridge ASM1184e. I have no idea how I didn’t see that before. I guess its the same on the Taichi Ultimate board. In conclusion, the Lanes seem to be split up like this:
On the Taichi Ultimate, 2 SATA ports are configured as PCIe 3.0 for 10G

  • 4 lanes for the 3rd pcie / 2nd m2 slot
  • 2 for the 5 Gbit LAN on the X370 Board / for the backpanel USB 3.1 on the Ultimate
  • 1 for the ASM1061 SATA controller
  • 1 for the ASM1184e PCIe switch connecting Wifi, Intel I211 LAN and the two PCIe x1 slots