What are PCIe x1 Slots Used For?

What is it and how can I use it? (With 1-slot GPUs, other connectors are visible, including one which is probably the old PCI connection

We'll break down the basics PCI Express logo What is PCIe Gen 4? PCIe Gen 4 is the fourth and latest generation of the PCI Express specification

pcie 8x slot A PCI slot is a built-in slot on a device that allows for the attachment of various hardware components such as network cards, modems, sound

pcie x16 slot A single PCI Express serial link is a dual-simplex connection It is clear that the PCI Express x16 adapter will not physically fit in the PCI x1 slot