New
#11
You can also install a x16 card into a x1 slot. A lot of x1 slots have the back portion removed just for that. You see PCI-E negotiates the requirements on startup.
PCI Express - Wikipedia, the free encyclopedia
Of course that is not overly common as most just use the x16 slot for all.A PCIe card fits into a slot of its physical size or larger (with ×16 as the largest used), but may not fit into a smaller PCIe slot; for example, a ×16 card may not fit into a ×4 or ×8 slot. Some slots use open-ended sockets to permit physically longer cards and negotiate the best available electrical and logical connection.