PCIe slots are commonly found on motherboards and offer extra expansion slots for graphics cards, sound cards, and other PCI devices. PCIe slots can also be used to install a second hard drive or SSD.
PCIe slots are often configured in a x16, x8, or x4 configuration. A x16 slot can accommodate a graphics card that is double the size of a regular card.
A x8 slot can accommodate a graphics card that is the same size as a regular card, and a x4 slot can accommodate a graphics card that is half the size of a regular card.
PCIe slots can also be used to install another hard drive or SSD.