Free System Programming Textbook (Illinois CS241)
Amazing school!  I was class of 2003.  It was a really great combination of hard computer science topics along side close to the metal programming.  I graduated proficient in Vim, C/C++, make, kernel driver development, digital control systems, networking AND complexity theory, algorithms, languages, error analysis, protocols, operating systems etc...  I got B’s, still somehow remember differential equations.  Couldn’t be happier with the result :)