PCIe slots are the connectors on a motherboard that allow you to attach additional PCIe devices. There are four sizes of PCIe slots, and each one is designed for a different type of device.
The first PCIe slot is the small M.2 slot, which is designed for storage devices like SSDs.
The second PCIe slot is the medium M.2 slot, which is designed for storage devices and graphics cards.
The third PCIe slot is the large M.
The fourth PCIe slot is the x1 slot, which is designed for basic input/output systems (BIOS) and other low-power devices.