ASROCK B450 Pro4 Handbuch Seite 28

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.
* If M2_1 is occupied, PCIE4 will be disabled.
PCIe Slot Configurations
Ryzen Series CPUs (Pinnacle Ridge)
Ryzen Series CPUs (Summit Ridge)
Ryzen Series CPUs (Raven Ridge)
26
PCIE2 PCIE4
x16 x4
x16 x4
x8 x4