Found in 2 comments on Hacker News
kingcharles · 2021-10-08 · Original thread
This is the book I learned from in the 90s: https://www.amazon.com/Developing-32-Bit-Operating-System-Cd...

It's basically "Writing an Operating System from Scratch for Dummies".

I actually wrote my own graphical x86 OS starting from the code in there.

Related: Source Code For MMURTL:

https://github.com/bproctor/MMURTL

Keywords: Richard A. Burgess "Developing your own 32-bit operating system"

Buy either of his two books on Amazon:

https://www.amazon.com/gp/product/0672306557

https://www.amazon.com/gp/product/1588530000

I remember this as a great book on OS'es, back in the day...