pci express - Special PCIe x8 in regular PCIe x16 slot? - Super User
Pci e x8 in x16 slot ? - Graphics Cards - Linus Tech Tips
PCIEX16E-844S | PCIe x16 edge connector to one PCIe x8 and two PCIe x4 Slots riser cable | x16 to x8 and x4 PCIe bifurcation riser cable | PCIEX16E-844S