The continous development of computer technology supported by the VLSI revolution stimulated the research in the field Β·of multiprocessors systems. The main motivation for the migration of design efforts from conventional architectures towards multiprocessor ones is the possibi I ity to obtain a significant processing power together with the improvement of price/performance, reliability and flexibility figures. Currently, such systems are moving from research laboratories to real field appl ications. Future technological advances and new generations of components are I ikely to further enhance this trend. This book is intended to provide basic concepts and design methodologies for engineers and researchers involved in the development of mul tiprocessor systems and/or of appl ications based on multiprocessor architectures. In addition the book can be a source of material for computer architecture courses at graduate level. A preliminary knowledge of computer architecture and logical design has been assumed in wri ting this book. Not all the problems related with the development of multiprocessor systems are addressed in th i s book. The covered range spans from the electrical and logical design problems, to architectural issues, to design methodologis for system software. Subj ects such as software development in a multiprocessor environment or loosely coupled multiprocessor systems are out of the scope of the book. Since the basic elements, processors and memories, are now available as standard integrated circuits, the key design problem is how to put them together in an efficient and reliable way.