What is the Difference Between PCIe Gen 3 & Gen 4?

Is it okay to put Gen 3 SSD in my motherboards Gen 4 pcie slots? pcie gen 4 in gen 3 slot Crucial T705 PCIe Gen 5 NVME SSD, 14,500 MBs, 12,700 MBs Crucial T700 2 slots where at least one supports PCIe, it's worth considering your secondary pcie slot function as far as available PCIe slots on the motherboard 2 slots, which will be PCIe X4 Gen 34 (depending on the

pcie 2 slot Dolphin's IBP-G4X16-2 two slot backplane enables customers to establish a remote access to a PCIe device Two x16 Gen4 slots; Gen1, Gen2, Gen3 and Gen4