Yeah, I always feel the same when I see similar things. How do you even start?
- Find some digitized assembly programming manuals from the time (I think the one I used was distributed with the Commodore 64, and ended up having several typos introduced by OCR).
- Write a tool to recognize, decode, and print out an operation when you feed it a little data
- You basically need to set up a loop of fetching instructions, interpreting them, then doing what they say. An actual CPU runs in a similar loop, and it generally doesn't stop until power is removed,
I think that after the classes I took, I read a lot of what other emulator writers said. This article is a basic look at the structure of an emulator, the theory behind them, and some different designs: http://fms.komkon.org/EMUL8/HOWTO.html
I don't understand why a basic understanding of CPU architectures isn't a CS fundamental everywhere.
Even if you have no interest in emulating a CPU or an OS, you really do need to know what registers are, how caches work, what interrupts do, and how basic IO happens.
At the very least it's a practical demonstration of one particular kind of VM, and - if you want to - you can generalise from that to VMs of your own design.
For web apps, not understanding these things can get expensive. Cycles, even cloud cycles, aren't free, and if you take zero interest in optimisation and efficiency you're literally throwing money away.