This textbook is about lower-level computer programming: machine language and assembly language, and how these languages are used in the typical computer system. This is meant to give the student a basic understanding of the fundamental concepts of the organization and operation of a computer. Even if the student never again programs in assembly language (and we would hope that they never have to ) it is important that they understand what the computer is doing at the machine language level. A good understanding of computer organization translates into a better understanding of the features and limitations of all computer facilities, since all systems must eventually rest on the underlying hardware machine. This text uses MIX, from Knuth's "The Art of Computer Programming".