That sounds like a lot of fun! I had a Heathkit myself, but it was an H89. As for ARM64, sure, but I'm not talking about ARM64, in case that wasn't just a rand

That sounds like a lot of fun! I had a Heathkit myself, but it was an H89. As for ARM64, sure, but I'm not talking about ARM64, in case that wasn't just a randomly chosen unmanageable architecture. Check out the VLSI ARM3. All 26 instructions are listed in Table 1 on the bottom of page 1–7 of the datasheet: https://www.chiark.greenend.org.uk/~theom/riscos/docs/ARM3-datasheet_ARM-Family-Data-Manual-VLSI.pdf https://www.chiark.greenend.org.uk/~theom/riscos/docs/ARM3-d... That's cheating a little bit because it doesn't include the addressing modes, conditionals, and bit shifts and rotations, because those are bitfields in other instructions, but even so, it's not cheating much. You can still learn the whole instruction set in an afternoon (though not half an hour!), and it's an instruction set that can be implemented much more efficiently than most ISAs before or since.