Recently, My Mac Mini G4 1.25G seems dead, I guess the failure point is HDD dead so I’m looking for howto check hardware in Open Firmware.
You can enter Open Firmware (BIOS) by pressing the key combination cmd-opt-O-F just as you power on a Macintosh. The cmd key is the one with the Apple logo, and the opt (option) key is the same as the alt key.
Command line editing (you can use ctrl-a to go to the beginning of a line, ctrl-e to go to the end, ctrl-u to erase a line, etc.)
Doskey (press the up-arrow key for history)
Other detail operations and diags. please refers to below link …