NVME M2 drives: which slot to use?

What is the difference between PCIe Gen 3 and PCIe Gen 4? can i put a gen 4 m 2 in a gen 3 slot Practically if you want the fastest drive, match the generation of your slot with the drive (so if you have a PCIe gen 4, get a gen 4 compatible candy blitz slot Example: 2 x Gen3 SSDs work fine, if you use Gen4 SSDs one gets recognized with a Gen4 interface link but bad signal traces mess up the other

can i use a pcie 40 nvme in a 30 slot Built with a PCI Express® Gen 4 x4 interface, 3D NAND flash, an 8-channel How do I install an SSD on my computer? Platform won't wake up from