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

4-3, per single PCI Segment Group show less , ECN, November 18, 2018 SMBus interface for SSD Socket 2 and Socket 3 SMBus interface signals are

My laptop has a gen 3 slot First of all, I know that a PCIe 4 SSD NVMe will be running at gen 3 speeds and bottlenecked by the PCIe 3 slot But

pcie 30 in 40 slot ssds Does such a low profile card exist that supports 4 drives? Click to expand PCI Express Gen 3 Carrier Board for 4 PCIe SSD

pcie 4 slot PCI Express Gen Bandwidth per line +------------------+------------------------------------+ PCIe Gen1