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Starting with the PowerBook 3400 and desktop Power Macintosh G3 computers, you can enter the Open Firmware user interface on the current machine via the keyboard and display without setting up a remote serial connection with a second computer. The process for invoking the Open Firmware user interface on the current machine is the same.
Startup the computer and simultaneously press the Command, Option, O, and F keys on its keyboard. Release the keys after you hear the boot sound from the computer and see the Open Firmware prompt. Power Macintosh G3 computers equipped with external serial ports also support remote connection to the Open Firmware user interface, as described in Invoking the User Interface Via Remote Connection.