Buy PCI Express X1 to X16 Low Profile Slot Extension

It's a slot of x16 size but electrically x4 This

1 Answer 1 Your assumption is correct This would be a slot with only four PCIe lanes connected, but it can fit a 16-lane card This is pretty

pcie 20 x16 slot PCIe boards can fit into slots designed for their lane configuration or higher Plugging a x4 PCIe into a x16 slot is acceptable

pcie 30 x4 slot Product Overview · This PCIe x1 to PCIe x16 Slot Extension adapter provides enhanced compatibility between motherboards and a variety of PCI-Express expansion