Asus Z9PE-D8 WS - Manual (Page 40)

2-18 Chapter 2: Hardware information
2.5.4 PCI Express x16 slot (x16 link)
The onboard PCIE 1 and 3 provide one x16 Gen3 link to CPU1 (Auto switch
to x8 link if PCIE 2 and 4 are occupied); The onboard PCIE 5 and 7 provide
one x16 Gen3 link to CPU2. These slots support VGA cards and various
server class high performance add-on cards.
2.5.5 PCI Express x16 slot (x8 link)
The onboard PCIE 6 provides one x8 Gen3 link to CPU2; The onboard PCIE
2 and 4 provide one x8 Gen3 link to CPU1. These slot support VGA Cards
and various server class high performance add-on cards.
PCIE 1 1 x PCI-E x 16 (Gen3 x16/ x8 link)
PCIE 2 1 x PCI-E x 16 (Gen3 x8 link)
PCIE 3 1 x PCI-E x 16 (Gen3 x16/ x8 link)
PCIE 4 1 x PCI-E x 16 (Gen3 x8 link)
PCIE 5 1 x PCI-E x 16 (Gen3 x16 link)
PCIE 6 1 x PCI-E x 16 (Gen3 x8 link)
PCIE 7 1 x PCI-E x 16 (Gen3 x16 link)