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

What is the difference between PCIe Gen 3 and PCIe Gen 4? pcie 4 in pcie 3 slot ssd PCI-E SSDs represent a significant leap in storage technology, offering enhanced speed and performance over previous PCI-E SSDs pcie slot cover 2x slots M2_1 slot - Supports PCIe x4

pcie slot cover A PCIe SSD card can be inserted into a motherboard having PCIe slots, but the SSD will not be able to make use of the greater bandwidth

pcie m2 slot 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 Your PCIe card will run at the lowest generation present So if you put a PCIe card in a PCIe slot, you'll get PCIe performance