Computer Science from the Bottom Up — A free, online book designed to teach computer science from the bottom end up. Topics covered include binary and binary logic, operating systems internals, toolchain fundamentals and system library fundamentals.
Warning: This book isn't about Computer Science as much as it is about Computers in general. That should be clear from the Table of Contents, though.
The book is incomplete in parts with lots of notes left ("XXX: go into more detail?"), but the parts which are complete are very useful. If nothing, you'll have a lot of material to Google!