ASROCK AB350 Pro4 Manual De Instrucciones página 26

2.4 Expansion Slots (PCI Express Slots)
There are 6 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 2.0 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 2.0 x1 slot) is used for PCI Express x1 lane width cards.
PCIE4 (PCIe 3.0 x16 slot) is used for PCI Express x4 lane width graphics cards.**
PCIE5 (PCIe 2.0 x1 slot) is used for PCI Express x1 lane width cards.
PCIE6 (PCIe 2.0 x1 slot) is used for PCI Express x1 lane width cards.
* PCIE2 will downgrade to x8 mode when A-Series APU is installed.
** PCIE4 will downgrade to x2 mode when A-Series APU is installed.
** If M2_1 is occupied, PCIE4 will be disabled.
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