[throwawayboise]

Sometime in the first half of the 1980s I had a TI99/4a, my first computer.

I started programming in BASIC and it was interesting but I felt I was missing a lot in my understanding of what was really going on.

At some point I found a program called "picoprocessor" that was along these lines, but vastly simpler of course. It created on the display an operator panel for a 4-bit computer, it had maybe 2 registers and only a few operations but it was enough to get the light bulb glowing in my head about how computers worked at the assembly language/machine code level.

Seeing the state changes visually on the "panel" as the program ran was so helpful to my understanding that I still remember the experience quite clearly some 40 years later.

My dad also commented about the computers in the lab where he worked, that had operator panels with toggle switches and LEDs. He could tell what loop the program was running by the pattern of lights on the panel.