ASROCK X299E-ITX/ac Manual Del Usuario página 22

2.4 Expansion Slot (PCI Express Slot)
There is 1 PCI Express slot 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 slot:
PCIE1 (PCIe 3.0 x16 slot) is used for PCI Express x16 lane width graphics cards.
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