Asus Z9NH-D12 - Manual (Page 40)

2-18 Chapter 2: Hardware information
2.5.3 PCI Express x16 slot (x16 link)
The onboard PCI Express x16 slot provides x16 link to the Intel ® Xeon E5-2400 family
processor. This slot supports VGA cards and various server class high performance
add-on cards.
PCIEx16 slot (x16 link)
When installing the motherboard to a 1U/2U rackmount server system, first install
the expansion card using an optional PCIe x16 riser card, then install the riser card
along with the expansion card to the onboard PCI Express x16 slot.