To install OS3.5 (or 3.9) that A1200 would need:
° A CD-ROM.
° 4 Mb Fast Ram.
° A 3.1 KS chip and
° A HDD.
A500s, A600s, and A2000s must have at least an 68020 cpu and 1Mb Chip Ram in addition to the above! (The 3.5 & 3.9 OSs come on CD)
The OS3.5 CD-ROM includes OS3.1 because THIS must be present for the 3.5 install to go ahead.