ArnoldLayne wrote:
Since every C64 and C128 uses an NMOS 6510 or derivative, it is guaranteed that software using illegal opcodes will run on every C64/C128. Some games use them, afaik Arkanoid. Of course, demos use them a lot. I also believe that GEOS uses them, but I am not 100% certain on this.
I wonder how well the emulators emulate the undocumented opcodes. That would be a good way to find out.