What is the purpose of the PCIe X1 slot

Take a look at this picture of a PCI-Express x1 slot that was cut out to allow down-plugging a PCIe x16

By specification, all PCIe cards are backwards compatible with the lowest bandwidth x1 lane slots If the x1 slot is designed with an open end,

x16pciexp slot 1 PCIe x16, 1 PCIe x16, 1 PCIe x1, 1 Key E for WiFi - 1 x PCI Express x1 Slot - Supports AMD Quad CrossFireX™ and CrossFireX

x16 slot What is a PCI Express x1 Slot? The smallest of the PCI Express slots, your standard PCI Express x1 slot is essentially your starting point for most expansion