Today we are accustomed to working with computers at a high level. That is, we write computer programs in high-level languages, use application programs, and work with an operating system without knowing what goes on under the hood. A fundamental relationship exists between computer hardware and many aspects of programming and software components in computer systems. As computer scientists, it is important that we understand how hardware interacts with software. By studying the internal workings of a computer, we hope to learn how the internal components of a computer are designed and constructed and how this affects the performance of the computer and the software applications.