Hardware/Expansion Interface

The EXpansion Interface (a.k.a. EXternal Interface, and EXI) is an SPI-like bus. On the GameCube, it is exposed via the Serial Ports and Memory Card slots, and is used internally for the IPL ROM + the RTC. On the Wii, it is exposed via the Memory Card slots, and used internally for a stripped down GameCube IPL + the Wii Hardware/RTC. The Wii Family Edition and Wii Mini are identical in this regard, but don't have the actual memory card slots (the traces for them exist though). The Wii U technically also has it, albeit only internally for the RTC.