What is the difference between PCIe GEN ⛑️

PCIe Card Under Test 12V DC from adapter supplied USB connector for factory configuration only x8 version of interposer shown here Host PCIe Slot Connecting

With full backward compatibility, PCIe provides the same topologies and channel reach for client and server configurations as in PCIe

pcie slot length PCIe Slots are backward compatible like most of the interfaces, which means that you can use any generation card on any generation slot But

pcie slot function PCIe Gen 3 was unable to accommodate the full bandwidth of high-speed PCIe NVMe SSDs This was effectively creating a bottleneck in SSD performance PCIe Gen 4