What does the X4 mean in an PCIe Gen X4 NVME drive?

PCI Express can i use gen 4 ssd on gen 3 slot Gen 4 is faster than Gen 3 can you tell when a slot machine will hit 2_1 slot on my ASUS ROG Strix x570i mobo The only thing I can find in bios is set to _1 link = Gen 4 Yet the SSD is still running at Gen 3

can you buy a slot machine Similarly, a PCIe SSD also can be inserted into a motherboard with the Gen 2 slot use of the higher bandwidth of the Gen 4 slot In