I wonder how many people actually read the books they were suggesting. Like here on HN, Art of Computer Programming gets mentioned a lot. But I've not met anyone who has actually read it. And I own a copy. It's so hard of a read that I am just going to assume anyone who says they did is either lying or Donald Knuth. I'm suspect of books as a means of information conveyance. They make great mediums for narratives, but…
To understand the first few hundred pages on mathematical preliminaries, the books "The Art and Craft of Problem Solving" by Zeitz and "Concepts of Modern Mathematics" by Stewart, were essential, both of which were recommended here in other book list posts. I also had already read the CS:APP book which covers x86-64 assembly so the MIX introduction was fairly straight forward. http://csapp.cs.cmu.edu/
A book for me that was hard to read, is this book: http://www.cs.cmu.edu/~rwh/pfpl.html Practical Foundations for Programming Languages each page I have to translate with the notation guide, and is a research exercise searching Wikipedia for additional material.