I did Ben Eater's 6502 kit and expanded on it a lot. You're right, it really gets you to appreciate how computers really work, in a much simplified way of cours

I did Ben Eater's 6502 kit and expanded on it a lot. You're right, it really gets you to appreciate how computers really work, in a much simplified way of course, compared even to for example the first IBM computer. Implementing something like a FAT file system for example also really makes you appreciate the deeper concepts of how an OS works. I only did a very simple FAT implementation, without subdirectories, but even with that, terms like FAT and sector became very concrete things instead of vague concepts.