It still is! It is one of those books most recommended in the osdev community as it explains theory and then shows how Minix did it (praxis), including its source code that can be consulted at any time, if one so desires. (I’m not reading it as part of a university course.)

One does feel its age a bit, though.

(Thought that something similar was said in Tanenbaum’s book, but it actually was a different book (Programming From The Ground Up, by Jonathan Barlett), have uploaded it anyway.)