@wingo Yes. I remember the days when if I *really* wanted to know what the computer was doing, because what the logic analyser was reporting didn't make sense, I could use an oscilloscope. We knew every byte of code in the machine and we had a reasonable idea what the hardware was.

I reckon it was things like on-chip caches that broke this way of doing software - the CPU was now doing things that weren't visible on the external bus.