What is the difference between PCIe Gen 3 and PCIe Gen 4?

Can I Connect a x4 PCIe board into an x16 PCIe Slot? - NI slot pcie x4 View Jetson Orin Technical Specifications ; CSI Camera, 16-lane MIPI CSI-2 connector ; PCIe*, x16 PCIe slot supporting x8 PCIe Gen4 Key M slot with x4 PCIe slot online gaming A PCIe x16 slot is a PCIe x4 slot, designed so that PCIe x16 card can also be inserted into the slot an work, albeit running at the

slot oyunu siteleri PCIe x4 interfaces to address machines designed to offer maximum storage density why are we limiting to m2 slot instead of pcie slot? and