Can I use a PCIE card in a PCI slot?

What are the top uses of PCIe x1 Slots? pcie expansion slot pcie lanes, pcie x16 slot, pcie x1 slot, pcie x4 slot, pcie x8 slot, which pcie slot to pcie slot gpu PCIe card in a single slot? According to the ATX specification, PC expansion slots have a pitch of inches which translates to

pcie 40 gpu in 30 slot Simply no Cards and slots are purposely designed in the way to prevent accidental inserting of wrong card into wrong slot · Them PCIe was