CPU Migration, one (Apple?) has done it right.

I am an old IT git (not GitHub related). This is only my view from what I have seen and know.

CPU migration is not new. The problem existed as soon as new hardware was available and manufacturers had to find a way to reuse old code without a full rewrite. Without this computer evolution would have been in my view far more slower.

Basically the Hardware guys would had to wait for the Software guys to be ready.

I believe one of the 1st to do this was IBM with their IBM System/360. They used ‘Binary translation’ to be able to run ‘old’ on ‘new’.

DEC, did the same thing with their Vax range. At the start, they could run PDP11 CPU by having basically dual instruction set. It was ‘silently’ removed later since not in use (as far as I know) as much.

Apple produced the Apple Mac with the 68k from Motorola and used various iteration of it. Up to 68040 if I recall in their Quadra Range. Having done assembler on various CPUs at the time (8051, Z80, 6502, 68k), it was my preferred CPU. Its (most) op-code was based on Octal format. Also it was 32 bits internally with a 16bits bus.

Then Apple decided to change CPU to Power PC due to various reasons (I believe one was supply). This was their 1st CPU migration.