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.
The IOP was primarily developed by BroadOn, and some of its functionality is described in an early 2005 patent published by BroadOn.
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.
The Wii's OTP and SEEPROM are also present in the Hollywood chip, and are interfaced with by the IOP for special functionality such as storing console-unique data.