What is in ROMS and Firmware?

[teroyk]

I started interesting what is available before Finder starts.

I found some interesting information about Open Firmware
Running files from a hard drive in Open Firmware:
https://developer.apple.com/library/archive/technotes/tn/tn2001.html
Apple Computer Open Firmware Home Page:
https://web.archive.org/web/20060708223126/http://bananajr6000.apple.com/
The Mac ROM Enters a New World:
https://www.fenestrated.net/mirrors/Apple%20Technotes%20(As%20of%202002)/tn/tn1167.html

But is this dropped in New World ROMs?
MicroBug: The ROM Debugger:
https://www.fenestrated.net/mirrors/Apple%20Technotes%20(As%20of%202002)/tn/tn1136.html

[Daniel]

MicroBug is a component of the 68k ROM. It only gets activated way into the boot process on 68k Macs, let alone PowerPC ones. By the time MicroBug is ready on a PowerPC machine, Open Firmware has already run, the Mac ROM has been loaded from disk (for NewWorld Macs), the Trampoline has run (also only for NewWorld), the NanoKernel and 68k Emulator have started, and the emulated 68k boot process has gotten far enough along to enable it.

"Before Finder starts" consists of several major phases, and MicroBug only shows up in the last one.