ASROCK X299 Extreme4 Manual Del Usuario página 20

2.4 Expansion Slots (PCI Express Slots)
There are 4 PCI Express slots on the motherboard.
Before installing an expansion card, please make sure that the power supply is
switched off or the power cord is unplugged. Please read the documentation of the
expansion card and make necessary hardware settings for the card before you start
the installation.
PCIe slots:
PCIE1 (PCIe 3.0 x1 slot) is used for PCI Express x1 lane width cards.
PCIE2 (PCIe 3.0 x16 slot) is used for PCI Express x16 lane width graphics cards.
PCIE3 (PCIe 3.0 x16 slot) is used for PCI Express x16 lane width graphics cards.
PCIE4 (PCIe 3.0 x16 slot) is used for PCI Express x4 lane width graphics cards.
* If you install CPU with 44 lanes, PCIE2/PCIE3/PCIE4 will run at x16/x16/x4.
* If you install CPU with 28 lanes, PCIE2/PCIE3/PCIE4 will run at x16/x8/x4.
* If you install CPU with 16 lanes, PCIE2/PCIE3/PCIE4 will run at x16/x0/x4 or x8/
x8/x4.
* If PCIE1 slot is occupied, M2_3 slot will be disabled.
PCIe Slot Configurations (For CPU with 44 PCIe lanes)
Single Graphics Card
Two Graphics Cards in
CrossFireX
Mode
18
PCIE2
x16
TM TM
x16
or SLI
PCIE3 PCIE4
N/A N/A
x16 N/A