They are complementary and not the same. I very highly recommend that you get and study "Computer Systems: A Programmer's Perspective, 3rd edition" since it is a very practical and detail oriented book(i.e. no hand-waving and full of code for x86-64) for the Programmer. Hennessy & Patterson's "Computer Organization and Design: The Hardware/Software Interface" is more high-level with not enough depth while their "Computer Architecture: A Quantitative Approach" is full on theory book.