I took plenty of OS and compiler classes in college and I was still struggling to grasp some concepts. I think the issue was I was able to understand each individual class in isolation, but when I tried linking everything together, something just didn't click.

I came upon this book/course: https://mitpress.mit.edu/books/elements-computing-systems-se...

From a Hacker News post IIRC, and it helped more than I can express. At least for me it filled in all the little gaps in the computing stack and really made me "get it". I could relate to the old timers complaining about how everything is so bloated now.

The course is very hands on and you build a "full stack" from logic gates to an operating system that can run programs. It's truly amazing, and I think I learned more from this book than most of my college courses.

I believe it's also offered for free on coursera and has a website: https://www.nand2tetris.org/

But if you really want to know how a full computer works from the ground up, I think this book would be well worth the time.