I had a softer core version of this with the first computer I personally owned, a Spectravideo MSX machine with a Z-80 processor. I had more than a hex pad, I h

I had a softer core version of this with the first computer I personally owned, a Spectravideo MSX machine with a Z-80 processor. I had more than a hex pad, I had a BASIC interpretter which included an actual manual. And I had a Z-80 assembly reference manual that my older brothers had liberated from the high school’s TRS-80 lab. The company itself was defunct and there was no deeper documentation of the system available (plus this was the pre-internet days so even if it were, finding it would be a challenge). I spent time peeking and poking data into every one of the computers 64K bytes of RAM and managed to find the memory which had the definitions of the displayed characters (and used this to allow me to type ä, ö, ü and ß for a drill and practice program I wrote for studying German). I also wrote part of a disassembler but never got around to handling the multi-byte opcodes of Z-80 assembly. This kind of low-level experimentation can really help you get your mind around what a system can do.