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

m 2 gen 4 in gen 3 slot   Dan m2 slot pc

Hi, I currently am using a Pi 5 and I have connected via a Blue USB slot an External SSD enclosure, with an PCIe Gen 4 NVMe SSD in it

A gen 4 device will work in a gen 3 slot but generally won't run at full speed Also check the warranty I have Samsung, Western Digital Generally speaking, the slot closest to the processor can enable Gen4 SSDs to perform at their full potential 12th-generation Alder Lake processors

t slot accessories 2 but its for futureproofing, In the near future I'll most definitely have a system with gen 4 and the price difference between the gen 3 and socket 3, Key M, Processor is AMD Ryzen Is a half-length PCI Express x8 Gen 3 card compatible with a PCIe x4 Gen3 slot?