It doesn't help that its not well named, realtime makes it sound fast.

One of the few things I remembered from my degree was the realtime programming course, because we got to program a model train set in Ada, on a 286(?), running on floppies. This was in ~2015, so ancient hardware even then, and it was slow, but it was "realtime".

Interestingly, my compsci degree never covered O notation, so that I've had to pick up along the way :/