A significant chunk of what the Dragon book covers is state machine theory, what you need to know if you're writing a compiler-compiler like yacc. The state of the art in code generation had moved on even for the edition I read in college back in 2004 or so, so the tail end of the book isn't super relevant. IMO it was never a good book for practical compiler implementation. It's better as an academic reference for compiler theory, especially DFA, NFA, PDA etc. construction.