This textbook provides an explanation from the ground up of how a computer system works and is designed, starting with circuits and ending with the operating system and its shell. Topics are taught through relatively sophisticated design projects in which the reader/student builds each component or at least a portion of it. The computer components are rudimentary but representative, in the way that one would learn the important aspects of how a car works by building a go-kart that can travel at 50mph. The descriptions of each computer component include coverage of why, in security terms, the various design choices are made. Once the computer is fully described, security holes in systems are covered, showing exactly where the problems occur, and what aspects of the system they exploit.