So, I have come with a small report to make.
Remember a year ago I used to have an issue booting from my 512GB PATA SSD on my Mac mini G4 1.5GHz, which led me to concoct
this workaround?
In my post, I say this:
Throughout the whole post, I assume the boot issue I have both with the IDE device and the external FireWire drive is that their capacity is past 128 GB, regardless of how you partition them, and that the same issue would be present with USB devices past that capacity, as well.
I'll refer to the >128GB devices as "Big Drives" and to the <=128GB devices as "Small Drives".
Turns out this whole assumption was 100% wrong, because I can directly boot from a 2048 GB (2TB) M.2 Samsung EVO 860 SATA SSD using a cheap, nameless, excellent-working
M.2-SATA-to-PATA/IDE adapter, on a different, 1.25Ghz mini (likely works on 1.5GHz minis, too).
This leaves me with the following conclusion: It was the
disk firmware of both the Super Talent PATA SSD and the LaCie FireWire HDD that prevented direct booting into Mac OS on the Mac mini.
Well, at least it's good to have my workaround for some of the otherwise-incompatible devices out there.
That SSD (and 1.5GHz mini) are still healthy and perfectly functional, with no single sign of wear or issues after extensive usage, with hundreds upon hundreds of GBs of data moved around and stored among hundreds of thousands of files.
Man. Direct booting is good. OS9 on a mini is also so good. They should seriously put them back into production,
now with 7448 processors instead, which are already OS9-compatible and Mac-mini-motherboard-compatible... (One can theoretically still buy the processor for around 500 USD brand new and solder it into the board + adjust core voltage, clock it to 2GHz and have it run even cooler than it already does, with 1MB of L2 cache instead of 512KB.)
The exact product names are MC7448HX1700LD and MC7448VU1700LD (RoHS-compliant version), and NXP (the manufacturer, who bought Freescale) points to resellers
here.
Note there are many other versions of the 7448 listed on that page, but they were confirmed to be stable only with lower clock speeds, so I only highlighted above the versions of interest (1.7GHz, easily reach 2.0GHz, can only go even higher with revised, epic cooling solutions).
How-to video (in case anyone has all the equipment + knowledge/expertise to try):
https://www.youtube.com/watch?v=SnpdLt4OIFs