Can someone explain me the PCI-E slot variations & sizes

PCIe compatibility and performance generates a LOT of confusion In Explaining PCIe Slots

I explain in this video the Types of PCIe slots, how you can identify them, and also what their

pcie 30 x4 slot Workstation class systems offer a x16 slot for graphics and a x4 slot for higher-end PCI Express peripheral devices, while the server class

pcie 40 in 30 slot PCI Express was introduced in 2002 as Third Generation IO , and by the mid-2000s, motherboards had at least one PCIe slot for graphics PCIe