That was my first "crack." I happened to run the game on an Atari computer, which makes sounds during disk I/O. I could hear the sectors, hear the fail, retry, then remaining sectors load.

So, count em up, open the door, listen for fail, close, go!

Didn't even need a single hex value to accomplish.

After that, I got into it on an Apple. Reading this brings back memories. That particular machine is a lot of fun, and it is fun because almost everything is software. Totally open.