From an outsider looking in there is some confusion about amiga os...
Amiga OS 1.x to 3.9 - is for 68000 based processors. 68010, 68020,68030,68040,68060. Most amiga software is written for these.
The original amiga line of computers.
Amiga OS4.0+ is for Power pc processors only.
Power pc was supposed to be the successor to the 68000 series of machines, or planned to be... After Amiga INC imploded, others stepped in to do this.
AROS is a freeware open source implementation of amiga os, originally designed for x86 processors but now available on many platforms...
MorphOS is another amiga os next gen system designed for power pc processors. It runs on custom older hardware created for it (pegasos) and
also some Mac g4 or less models...
You may also check out AROS vision for your amiga 1200.