Function: They provide a way to connect a computer to a high-speed wired network or add various other capabilities not built into the motherboard.
Types: PCI (Peripheral Component Interconnect) is an older standard, while PCI Express (PCI-E or PCIe) is a newer, faster standard used in most modern computers.
FireWire: FireWire (also known as IEEE 1394) is an interface standard used for high-speed data transfer, often for connecting video cameras or external hard drives.