PCIe, or Peripheral Component Interconnect Express, is a high-speed serial computer expansion bus standard. It connects various components like graphics cards, storage devices, and network cards to the motherboard through dedicated point-to-point links. Unlike older parallel bus systems, PCIe uses serial communication which allows for higher speeds and better scalability.
The PCIe link training process consists of several phases. First is the Detect phase, where devices check for the presence of a link partner. Then comes Polling, where devices exchange training sequences to establish communication parameters. The Configuration phase negotiates link width and speed. Finally, the link enters L0 state for normal operation with active data transfer.