This book provides the theory and some examples of rule based reasoning applied to computer design. The presentation begins with design methods. These include both structured, object oriented design applied to software and systems engineering using several examples. Rule based reasoning, fuzzy logic, and new methods of virtual prototyping of computer designs are also covered.Virtual prototyping, in contrast to hardware prototyping, offers the promise of much lower design cost and more time to prepare prototypes. A discussion on this topic concludes with a sample implementation of these methods that can be used for computer system design.