What are the functions of pci extension?

Pci is a standard for defining local bus, which has the characteristics of plug and play. To put it bluntly, it's where you turn on the computer and plug in the graphics card. The supported PCI expansion slots can reach 10. Generally, there is a small motherboard, which can be plugged into an independent graphics card. Of course, it can also be different, such as restore card, sound card, network card and other independent expansion accessories.