Actually, I meant "Disassembler Installed". For whatever reason when the HD20 loads under System 2.0/Finder 4.1 that is the onscreen message. Apple shows it as an uncommon error code.
Obviously the HD20 INIT is not supposed to work with an MFS only system, but I am at a loss to explain why that message is called, or why it works at all. Looking at the Apple error table, since the HD20 INIT was supposedly unknown to the earlier System, it may have used the same error code as the disassembler and in later System versions the disassembler error code changed to a different number, however odd that seems.
I am anxious to try version 1.0 of the HD20 INIT and see if it manifests any differently as well as possibly working on the 128K, but I seem to recall reading that the version change represented just a bug fix. I did test v1.1 of the HD20 INIT on System .97/Finder 1.0 and it did not load. So that really only leaves S1.1/F1.1g. There is of course the possibility of testing different Finders with different system releases. It now occurs to me why using the HD20 INIT in an earlier system/finder didn't happen or occur to others at the time. If this combo will let an MFS system see an 800K disk, will it let it see the HD20 Hard Disk itself? If so, how stable would it be? Would this allow the HD20 Hard Disk to reliably operate as a 20MB MFS formatted hard disk? Would it allow an HD20 attached 800K external disk drive to work as an MFS volume as well? Anyone with a working HD20 HD should check this out for sure! If it does work, you'd be locked into a very early system environment, but heck as far as the stock 512K is concerned, that's just as well.