The system software that comes with the iBook computer is Mac OS 9 with the addition of the extensions and control panels required for product-specific features. For more information, see the references in Mac OS 9.
Like the system software on other Macintosh models since the introduction of the iMac, system software for the iBook has Open Firmware booting and Mac OS ROM in RAM. For more information, see the references in Open Firmware and ROM-in-RAM Architecture.