This book is about the structure and function of computers. Its purpose is to present, as clearly and completely as possible, the nature and characteristics of modern-day computer systems. This task is challenging for several reasons. First, there is a tremendous variety of products that can rightly claim the name of computer, from single-chip microprocessors costing a few dollars to supercomputers costing tens of millions of dollars. Variety is exhibited not only in cost, but in size, performance, and application. Second, the rapid pace of change that has always characterized computer technology continues with no letup. These changes cover all aspects of computer technology, from the underlying integrated circuit technology used to construct computer components, to the increasing use of parallel organization concepts in combining those components. In spite of the variety and pace of change in the computer field, certain fundamental concepts apply consistently throughout. The application of these concepts depends on the current state of the technology and the price/performance objectives of the designer. The intent of this book is to provide a thorough discussion of the fundamentals of computer organization and architecture and to relate these to contemporary design issues. The subtitle suggests the theme and the approach taken in this book. It has always been important to design computer systems to achieve high performance, but never has this requirement been stronger or more difficult to satisfy than today. A11 of the basic performance characteristics of computer systems, including processor speed, memory speed, memory capacity, and interconnection data rates, are increasing rapidly. Moreover, they are increasing at different rates. This makes it difficult to design a balanced system that maximizes the performance and utilization of all elements. Thus, computer design increasingly becomes a game of changing the structure or function in one area to compensate for a performance mismatch in another area. We will see this game played out in numerous design decisions throughout the book. A computer system, like any system, consists of an interrelated set of components. The system is best characterized in terms of structure the way in which components are interconnected-and function the operation of the individual components. Furthermore, a computer's organization is hierarchical. Each major component can be further described by decomposing it into its major subcomponents and describing their structure and function. For clarity and ease of understanding, this hierarchical organization is described in this book from the top down: Computer System: Major components are processor, memory, and I/O. Processor: Major components are control unit, registers, ALU, and instruction execution unit. Control Unit: Major components are control memory, microinstruction sequencing logic, and registers. The objective is to present the material in a fashion that keeps new material in a clear context. This should minimize the chance that the reader will get lost and should provide better motivation than a bottom-up approach. Throughout the discussion, aspects of the system are viewed from the points of view of both architecture (those attributes of a system visible to a machine language programmer) and organization (the operational units and their interconnections that realize the architecture). EXAMPLE SYSTEMS This book uses examples from a number of different machines to clarify and reinforce the concepts being presented. Many, but by no means all, of the examples are drawn from two computer families: the Intel Pentium 4, and the IBM/Motorola PowerPC. These two systems together encompass most of the current computer design trends. The Pentium 4 is essentially a complex instruction set computer (CISC) with some RISC features, while the PowerPC is essentially a reduced instruction set computer (RISC). Both systems make use of superscalar design principles and both support multiple processor configurations. PLAN OF THE TEXT The book is organized into five parts: Part One Overview: This part provides a preview and context for the remainder of the book. Part Two The Computer System: A computer system consists of processor, memory, and I/O modules, plus the interconnections among these major components. With the exception of the processor, which is sufficiently complex to be explored in Part Three, this part examines each of these elements in turn. Part Three The Central Processing Unit: The CPU consists of a control unit, registers, the arithmetic and logic unit, the instruction execution unit, and the interconnections among these components. Architectural issues, such as instruction set design and data types, are covered. Part Three also looks at organizational issues, such as pipelining. Part Four The Control Unit: The control unit is that part of the processor that activates the various components of the processor. This part looks at the functioning of the control unit and its implementation using microprogramming. Part Five Parallel Organization: This final part looks at some of the issues involved in multiple processor and vector processing organizations. The book also includes an extensive glossary, a list of frequently used acronyms, and a bibliography. Each chapter includes homework problems, review questions, a list of key words, suggestions for further reading, and recommended Web sites. A more detailed, chapter-by-chapter summary of each part appears at the beginning of that part. INTENDED AUDIENCE The book is intended for both an academic and a professional audience. As a textbook, it is intended as a one- or two-semester undergraduate course for computer science, computer engineering, and electrical engineering majors. It covers all the topics in CS 220 Computer Architecture, which is one of the core subject areas in the IEEE/ACM Computer Curricula 2001 JTFOl. For the professional interested in this field, the book serves as a basic reference volume and is suitable for self-study. INTERNET SERVICES FOR INSTRUCTORS AND STUDENTS There is a Web site for this book that provides support for students and instructors. The site includes links to other relevant sites, copies of the figures and tables from the book in PDF (Adobe Acrobat) format, and sign-up information for the book's Internet mailing list. The Web page is at WilliamStallings.com/COA6e.html; see the section, "Web Site for Computer Organization and Architecture, Sixth Edition", preceding this Preface, for more information. An Internet mailing list has been set up so that instructors using this book can exchange information, suggestions, and questions with each other and with the author. As soon as typos or other errors are discovered, an errata list for this book will be available at [A HREF="http://www.WilliamStallings.com"> WilliamStallings.com . In addition, the Computer Science Student Resource site, at WilliamStallings.com/StudentSupport.html , provides documents, information, and useful links for computer science students and professionals. PROJECTS FOR TEACHING COMPUTER ORGANIZATION AND ARCHITECTURE For many instructors, an important component of a computer organization and architecture course is a project or set of projects by which the student gets hands-on experience to reinforce concepts from the text. This book provides an unparalleled degree of support for including a projects component in the course. The instructor's manual not only includes guidance on how to assign and structure the projects, but also includes a set of suggested projects that covers a broad range of topics from the text: Research projects: The manual includes a series of assignments that instruct the student to research a particular topic on the Web or in the literature, and write a report. Simulation projects: The manual provides support for the use of the two simulation packages: SimpleScalar can be used to explore computer organization and architecture design issues. SMPCache provides a powerful educational tool for examining cache design issues for symmetric multiprocessors. Reading/report assignments: The manual includes a list of papers in the literature, one or more for each chapter, that can be assigned for the student to read and then write a short report. See Appendix C for details. WHAT'S NEW IN THE SIXTH EDITION In the three years since the fifth edition of this book was published, the field has seen continued innovations and improvements. In this new edition, I try to capture these changes while maintaining a broad and comprehensive coverage of the entire field. To begin this process of revision, the fifth edition of this book was extensively reviewed by a number of professors who teach the subject. In addition, a number of professionals working in the field reviewed individual chapters. The result is that, in many places, the narrative has been clarified and tightened, and illustrations have been improved. Also, a number of new "field-tested" problems have been added. Beyond these refinements to improve pedagogy and user friendliness, there have been substantive changes throughout the book. Roughly the same chapter organization has been retained, but much of the material has been revised and new material has been added. Some of the most noteworthy changes are the following: IA-64/Itanium architecture: This new architecture includes such important concepts as predicated execution and speculative loading. This edition features a chapter-length description and analysis. Cache memory: Cache memory is a central element in the design of high-performance processors, and cache design has become increasingly complex. An entire chapter is devoted to this issue in the new edition. Optical memory: The material on optical memory has been expanded and updated. Advanced DRAM architecture: More material has been added to cover this topic, including an updated discussion of SDRAM and RDRAM. SMPs, clusters, and NUMA systems: The chapter on parallel ...