The iMac Firmware Update 4.1.9 will only run on iMac computers with slot-loading CD or DVD drives running Mac OS 9.1 or later from a local drive. If you are using Mac OS X you must boot from a local Mac OS 9.1 or later writeable partition (not a CD, or network disk) prior to following the update instructions.
What's new in this version:
Includes improvements to starting up Mac OS X from the local hard disk, Firewire target disk mode, starting up from the local hard disk, network startup, and system stability. This update also adds support for additional security options which allow the Open Firmware to be password protected.