Mac128, if I connect my 800k drive to my HD20 and the HD20 to the Mac and then power on the HD20 for 30 seconds and finally switch on the Mac, I can boot off your "magic" System 2.0 floppy in the internal 400k drive until the Welcome to Macintosh box appears. At that point, the "Disassembler Installed" message appears inside the Welcome to Macintosh box and my 800k drive's LED flashes once (showing the HD20 INIT has loaded successfully). The HD20 then begins to audibly access as if it was going to boot, which is a normal part of the HD20 INIT's switching control of the boot sequence from the 400k floppy to the HD20. Unfortunately, the Welcome to Macintosh box starts flickering rapidly at this point and stays that way indefinitely (i.e., crash) and the HD20 stops accessing/booting.
I don't think this has anything to do with the fact I have System 4.2 and Finder 6.0 on my HD20. I think it simply is evidence that System 2.0 and Finder 4.1 are too old for the HD20's controller to handle the HD20-INIT's boot changeover process.
To verify, I tried my own System 2.0 and Finder 4.1 disk (the one that shows "Hard Disk 20 Startup" in the Welcome to Macintosh dialog and cannot make 800k MFS disks). It too freezes at the same place. So this lends evidence to the fact that System 2.0 is perhaps too old for the HD20's liking.
Now, if I switch off the HD20 but leave my 800k drive connected to the HD20, and the HD20 still connected to my Mac; and if I then boot once again from Mac128's magic System 2.0 floppy, I get the Disassembler Installed message in the Welcome to Macintosh box but the floppy boots to the Finder. And at the Finder I found that I was able to format 800k floppies as MFS. So while my HD20 would not boot, the fact that I could still use my 800k drive via the switched-off HD20 shows something, I guess.
Anyway, it's clear that more than just the HD20 INIT is required to boot the HD20 hard drive on a Mac 512k with 64k ROMs -- it requires a modern enough System (and possibly Finder).
I don't think this has anything to do with the fact I have System 4.2 and Finder 6.0 on my HD20. I think it simply is evidence that System 2.0 and Finder 4.1 are too old for the HD20's controller to handle the HD20-INIT's boot changeover process.
To verify, I tried my own System 2.0 and Finder 4.1 disk (the one that shows "Hard Disk 20 Startup" in the Welcome to Macintosh dialog and cannot make 800k MFS disks). It too freezes at the same place. So this lends evidence to the fact that System 2.0 is perhaps too old for the HD20's liking.
Now, if I switch off the HD20 but leave my 800k drive connected to the HD20, and the HD20 still connected to my Mac; and if I then boot once again from Mac128's magic System 2.0 floppy, I get the Disassembler Installed message in the Welcome to Macintosh box but the floppy boots to the Finder. And at the Finder I found that I was able to format 800k floppies as MFS. So while my HD20 would not boot, the fact that I could still use my 800k drive via the switched-off HD20 shows something, I guess.
Anyway, it's clear that more than just the HD20 INIT is required to boot the HD20 hard drive on a Mac 512k with 64k ROMs -- it requires a modern enough System (and possibly Finder).