The IOP, more commonly known in the Wii homebrew community as the Starlet, is an ARM core inside the Wii's Hollywood chip which handles I/O and security functions for the Wii. The IOP is responsible for controlling most of the Wii's hardware and software features which were not present on the GameCube, such as WiFi/Bluetooth support, NAND flash management, and title management (ES). The IOP also handles disc access when the system is running in Wii mode.
Main article: IOS
IOP-OS, commonly abbreviated to IOS, is the official BroadOn/Nintendo OS running on the IOP. It controls the IOP's functionality and communication with the Broadway. A homebrew alternative to IOS, "MINI", has also been made to allow for the creation of completely original Wii software without any dependence on Nintendo/BroadOn code.