I've worked on the compilers for Z systems and on the z/PDT emulator that someone else mentioned. The processors they run are indeed monsters. The instruction s

I've worked on the compilers for Z systems and on the z/PDT emulator that someone else mentioned. The processors they run are indeed monsters. The instruction set is especially interesting as you can see the transition from 24-31-64 bit. Messing around with the SAM (set address mode) instructions was always fun. They also have some interesting interruptable instructions that can move or compare up to 2GB of memory.