the M was added to differentiate macintosh models
i was told this by ACARD staff years ago when they sent me one of the last sata-raid PCI cards they had left
Interesting and maybe they are right.
I just never paid attention to that. At the time of pre-production we just flashed what was available.
Later we did not follow up how these were marketed.
Since you have several legacy G4-s, would it be possible to test in a non-MDD Mac, does a PC-based (non-Mac) Promise PDC20268 / PDC20269 / PDC20270 show up in Open Firmware tree?
Here none of them shows up in my MDD (1 GHz dual, FW400 ports).
But no problem in a 2009 MacPro, via PCI to PCI-e adapter board.