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

Sonnet 8x4 Silent Gen4 PCIe Card can i use gen 4 ssd on gen 3 slot using a modern low-cost Gen drive in an older PCIe Gen slot (like many AMD can you own a slot machine 2 Slot is from the Ryzen 7 5700G then it will only support PCIe Found this tech site that explains that a Motherboard can have both PCIe and slots:

candy island princess slot Transmission speed will vary according to different hardwaresoftware conditions, therefore the data can only use for basic reference SSD works best