Motherboard pci express x16 slot specification details explained in

PCI Express pci e x16 slot An increased number of lanes usually translates to a larger slot So a card that needs PCIe x16 cannot fit into a slot with fewer lanes But a pcie 4 slot PCIe slots allow your motherboard to connect with your PC's most critical components and provide key functionality

pcie 40 in pcie 30 slot Every PCIe slot supports its own number of CPU lanes X16 has 16 Lanes support, X8 has 8 Lanes support, X4 has 4 lanes support and x1 has