Computer Architecture: A Quantitative Approach by John L. Hennessy and David A. Patterson

1. www.dbeBooks.com - An Ebook Library 2. In Praise of Computer Architecture: A Quantitative Approach Fourth Edition The multiprocessor is here and it can no longer be avoided. As we bid farewell to single-core processors and move into the chip multiprocessing age, it is great timing for a new edition of Hennessy and Pattersons classic. Few books have had as signicant an impact on the way their discipline is taught, and the current edition will ensure its place at the top for some time to come. Luiz Andr Barroso, Google Inc. What do the following have in common: Beatles tunes, HP calculators, choco- late chip cookies, and Computer Architecture? They are all classics that have stood the test of time. Robert P. Colwell, Intel lead architect Not only does the book provide an authoritative reference on the concepts that all computer architects should be familiar with, but it is also a good starting point for investigations into emerging areas in the eld. Krisztin Flautner, ARM Ltd. The best keeps getting better! This new edition is updated and very relevant to the key issues in computer architecture today. Plus, its new exercise paradigm is much more useful for both students and instructors. Norman P. Jouppi, HP Labs Computer Architecture builds on fundamentals that yielded the RISC revolution, including the enablers for CISC translation. Now, in this new edition, it clearly explains and gives insight into the latest microarchitecture techniques needed for the new generation of multithreaded multicore processors. Marc Tremblay, Fellow & VP, Chief Architect, Sun Microsystems This is a great textbook on all key accounts: pedagogically superb in exposing the ideas and techniques that dene the art of computer organization and design, stimulating to read, and comprehensive in its coverage of topics. The rst edition set a standard of excellence and relevance; this latest edition does it again. Milos Ercegovac, UCLA Theyve done it again. Hennessy and Patterson emphatically demonstrate why they are the doyens of this deep and shifting eld. Fallacy: Computer architecture isnt an essential subject in the information age. Pitfall: You dont need the 4th edition of Computer Architecture. Michael D. Smith, Harvard University 3. Hennessy and Patterson have done it again! The 4th edition is a classic encore that has been adapted beautifully to meet the rapidly changing constraints of late-CMOS-era technology. The detailed case studies of real processor products are especially educational, and the text reads so smoothly that it is difcult to put down. This book is a must-read for students and professionals alike! Pradip Bose, IBM This latest edition of Computer Architecture is sure to provide students with the architectural framework and foundation they need to become inuential architects of the future. Ravishankar Iyer, Intel Corp. As technology has advanced, and design opportunities and constraints have changed, so has this book. The 4th edition continues the tradition of presenting the latest in innovations with commercial impact, alongside the foundational concepts: advanced processor and memory system design techniques, multithreading and chip multiprocessors, storage systems, virtual machines, and other concepts. This book is an excellent resource for anybody interested in learning the architectural concepts underlying real commercial products. Gurindar Sohi, University of WisconsinMadison I am very happy to have my students study computer architecture using this fan- tastic book and am a little jealous for not having written it myself. Mateo Valero, UPC, Barcelona Hennessy and Patterson continue to evolve their teaching methods with the changing landscape of computer system design. Students gain unique insight into the factors inuencing the shape of computer architecture design and the potential research directions in the computer systems eld. Dan Connors, University of Colorado at Boulder With this revision, Computer Architecture will remain a must-read for all computer architecture students in the coming decade. Wen-mei Hwu, University of Illinois at UrbanaChampaign The 4th edition of Computer Architecture continues in the tradition of providing a relevant and cutting edge approach that appeals to students, researchers, and designers of computer systems. The lessons that this new edition teaches will continue to be as relevant as ever for its readers. David Brooks, Harvard University With the 4th edition, Hennessy and Patterson have shaped Computer Architec- ture back to the lean focus that made the 1st edition an instant classic. Mark D. Hill, University of WisconsinMadison 4. Computer Architecture A Quantitative Approach Fourth Edition 5. John L. Hennessy is the president of Stanford University, where he has been a member of the faculty since 1977 in the departments of electrical engineering and computer science. Hen- nessy is a Fellow of the IEEE and ACM, a member of the National Academy of Engineering and the National Academy of Science,and a Fellow of the American Academy of Arts and Sciences. Among his many awards are the 2001 Eckert-Mauchly Award for his contributions to RISC technology, the 2001 Seymour Cray Computer Engineering Award, and the 2000 John von Neu- mann Award, which he shared with David Patterson. He has also received seven honorary doctorates. In 1981,he started the MIPS project at Stanford with a handful of graduate students.After completing the project in 1984,he took a one-year leave from the university to cofound MIPS Com- puter Systems,which developed one of the rst commercial RISC microprocessors.After being acquired by Silicon Graphics in 1991, MIPS Technologies became an independent company in 1998,focusing on microprocessors for the embedded marketplace. As of 2006,over 500 million MIPS microprocessors have been shipped in devices ranging from video games and palmtop computers to laser printers and network switches. David A. Patterson has been teaching computer architecture at the University of California, Berkeley, since joining the faculty in 1977, where he holds the Pardee Chair of Computer Sci- ence.His teaching has been honored by the Abacus Award from Upsilon Pi Epsilon, the Distin- guished Teaching Award from the University of California, the Karlstrom Award from ACM, and the Mulligan Education Medal and Undergraduate Teaching Award from IEEE. Patterson received the IEEE Technical Achievement Award for contributions to RISC and shared the IEEE Johnson Information Storage Award for contributions to RAID. He then shared the IEEE John von Neumann Medal and the C & C Prize with John Hennessy.Like his co-author, Patterson is a Fellow of the American Academy of Arts and Sciences,ACM,and IEEE,and he was elected to the National Academy of Engineering,the National Academy of Sciences, and the Silicon Valley En- gineering Hall of Fame. He served on the Information Technology Advisory Committee to the U.S.President, as chair of the CS division in the Berkeley EECS department, as chair of the Com- puting Research Association,and as President of ACM.This record led to a Distinguished Service Award from CRA. At Berkeley, Patterson led the design and implementation of RISC I, likely the rst VLSI reduced instruction set computer.This research became the foundation of the SPARC architecture, cur- rently used by Sun Microsystems, Fujitsu, and others. He was a leader of the Redundant Arrays of Inexpensive Disks (RAID) project,which led to dependable storage systems from many companies.He was also involved in the Network of Workstations (NOW) project,which led to cluster technology used by Internet companies.These projects earned three dissertation awards from the ACM. His current research projects are the RAD Lab, which is inventing technology for reliable, adaptive, distributed Internet services, and the Research Accelerator for Multiple Proces- sors (RAMP) project, which is developing and distributing low-cost, highly scalable, parallel computers based on FPGAs and open-source hardware and software. 6. Computer Architecture A Quantitative Approach Fourth Edition John L. Hennessy Stanford University David A. Patterson University of California at Berkeley With Contributions by Andrea C. Arpaci-Dusseau University of WisconsinMadison Remzi H. Arpaci-Dusseau University of WisconsinMadison Krste Asanovic Massachusetts Institute of Technology Robert P. Colwell R&E Colwell & Associates, Inc. Thomas M. Conte North Carolina State University Jos Duato Universitat Politcnica de Valnciaand Simula Diana Franklin California Polytechnic State University, San Luis Obispo David Goldberg Xerox Palo Alto Research Center Wen-mei W. Hwu University of Illinois at UrbanaChampaign Norman P. Jouppi HP Labs Timothy M. Pinkston University of Southern California John W. Sias University of Illinois at UrbanaChampaign David A. Wood University of WisconsinMadison Amsterdam Boston Heidelberg London New York Oxford Paris San Diego San Francisco Singapore Sydney Tokyo 7. Publisher Denise E. M. Penrose Project Manager Dusty Friedman, The Book Company In-house Senior Project Manager Brandy Lilly Developmental Editor Nate McFadden Editorial Assistant Kimberlee Honjo Cover Design Elisabeth Beller and Ross Carron Design Cover Image Richard IAnsons Collection: Lonely Planet Images Composition Nancy Logan Text Design: Rebecca Evans & Associates Technical Illustration David Ruppe, Impact Publications Copyeditor Ken Della Penta Proofreader Jamie Thaman Indexer Nancy Ball Printer Maple-Vail Book Manufacturing Group Morgan Kaufmann Publishers is an Imprint of Elsevier 500 Sansome Street, Suite 400, San Francisco, CA 94111 This book is printed on acid-free paper. 1990, 1996, 2003, 2007 by Elsevier, Inc. All rights reserved. Published 1990. Fourth edition 2007 Designations used by companies to distinguish their products are often claimed as trademarks or reg- istered trademarks. In all instances in which Morgan Kaufmann Publishers is aware of a claim, the product names appear in initial capital or all capital letters. Readers, however, should contact the appropriate companies for more complete information regarding trademarks and registration. Permissions may be sought directly from Elseviers Science & Technology Rights Department in Oxford, UK: phone: (+44) 1865 843830, fax: (+44) 1865 853333, e-mail: permissions@elsevier. com. You may also complete your request on-line via the Elsevier Science homepage (http:// elsevier.com), by selecting Customer Support and then Obtaining Permissions. Library of Congress Cataloging-in-Publication Data Hennessy, John L. Computer architecture : a quantitative approach / John L. Hennessy, David A. Patterson ; with contributions by Andrea C. Arpaci-Dusseau . . . [et al.]. 4th ed. p.cm. Includes bibliographical references and index. ISBN 13: 978-0-12-370490-0 (pbk. : alk. paper) ISBN 10: 0-12-370490-1 (pbk. : alk. paper) 1. Computer architecture. I. Patterson, David A. II. Arpaci-Dusseau, Andrea C. III. Title. QA76.9.A73P377 2006 004.2'2dc22 2006024358 For all information on all Morgan Kaufmann publications, visit our website at www.mkp.com or www.books.elsevier.com Printed in the United States of America 06 07 08 09 10 5 4 3 2 1 8. To Andrea, Linda, and our four sons 9. ix I am honored and privileged to write the foreword for the fourth edition of this most important book in computer architecture. In the rst edition, Gordon Bell, my rst industry mentor, predicted the books central position as the denitive text for computer architecture and design. He was right. I clearly remember the excitement generated by the introduction of this work. Rereading it now, with signicant extensions added in the three new editions, has been a pleasure all over again. No other work in computer architecturefrankly, no other work I have read in any eldso quickly and effortlessly takes the reader from igno- rance to a breadth and depth of knowledge. This book is dense in facts and gures, in rules of thumb and theories, in examples and descriptions. It is stuffed with acronyms, technologies, trends, formulas, illustrations, and tables. And, this is thoroughly appropriate for a work on architecture. The architects role is not that of a scientist or inventor who will deeply study a particular phenomenon and create new basic materials or techniques. Nor is the architect the craftsman who masters the handling of tools to craft the nest details. The architects role is to combine a thorough understanding of the state of the art of what is possible, a thorough understanding of the historical and current styles of what is desirable, a sense of design to conceive a harmonious total system, and the condence and energy to marshal this knowledge and available resources to go out and get something built. To accomplish this, the architect needs a tremendous density of information with an in-depth understanding of the fundamentals and a quantitative approach to ground his thinking. That is exactly what this book delivers. As computer architecture has evolvedfrom a world of mainframes, minicomputers, and microprocessors, to a world dominated by microprocessors, and now into a world where microprocessors themselves are encompassing all the complexity of mainframe computersHennessy and Patterson have updated their book appropriately. The rst edition showcased the IBM 360, DEC VAX, and Intel 80x86, each the pinnacle of its class of computer, and helped introduce the world to RISC architecture. The later editions focused on the details of the 80x86 and RISC processors, which had come to dominate the landscape. This latest edition expands the coverage of threading and multiprocessing, virtualization Foreword by FredWeber,President and CEO of MetaRAM, Inc. 10. x I Computer Architecture and memory hierarchy, and storage systems, giving the reader context appropriate to todays most important directions and setting the stage for the next decade of design. It highlights the AMD Opteron and SUN Niagara as the best examples of the x86 and SPARC (RISC) architectures brought into the new world of multiprocessing and system-on-a-chip architecture, thus grounding the art and science in real-world commercial examples. The rst chapter, in less than 60 pages, introduces the reader to the taxono- mies of computer design and the basic concerns of computer architecture, gives an overview of the technology trends that drive the industry, and lays out a quantitative approach to using all this information in the art of computer design. The next two chapters focus on traditional CPU design and give a strong grounding in the possibilities and limits in this core area. The nal three chapters build out an understanding of system issues with multiprocessing, memory hierarchy, and storage. Knowledge of these areas has always been of critical importance to the computer architect. In this era of system-on-a-chip designs, it is essential for every CPU architect. Finally the appendices provide a great depth of understanding by working through specic examples in great detail. In design it is important to look at both the forest and the trees and to move easily between these views. As you work through this book you will nd plenty of both. The result of great architecture, whether in computer design, building design or textbook design, is to take the customers requirements and desires and return a design that causes that customer to say, Wow, I didnt know that was possible. This book succeeds on that measure and will, I hope, give you as much pleasure and value as it has me. 11. xi Foreword ix Preface xv Acknowledgments xxiii Chapter 1 Fundamentals of Computer Design 1.1 Introduction 2 1.2 Classes of Computers 4 1.3 Dening Computer Architecture 8 1.4 Trends in Technology 14 1.5 Trends in Power in Integrated Circuits 17 1.6 Trends in Cost 19 1.7 Dependability 25 1.8 Measuring,Reporting,and Summarizing Performance 28 1.9 Quantitative Principles of Computer Design 37 1.10 Putting It All Together:Performance and Price-Performance 44 1.11 Fallacies and Pitfalls 48 1.12 Concluding Remarks 52 1.13 Historical Perspectives and References 54 Case Studies with Exercises by Diana Franklin 55 Chapter 2 Instruction-Level Parallelism and Its Exploitation 2.1 Instruction-Level Parallelism:Concepts and Challenges 66 2.2 Basic Compiler Techniques for Exposing ILP 74 2.3 Reducing Branch Costs with Prediction 80 2.4 Overcoming Data Hazards with Dynamic Scheduling 89 2.5 Dynamic Scheduling:Examples and the Algorithm 97 2.6 Hardware-Based Speculation 104 2.7 Exploiting ILP Using Multiple Issue and Static Scheduling 114 Contents 12. xii I Contents 2.8 Exploiting ILP Using Dynamic Scheduling, Multiple Issue, and Speculation 118 2.9 Advanced Techniques for Instruction Delivery and Speculation 121 2.10 Putting It All Together:The Intel Pentium 4 131 2.11 Fallacies and Pitfalls 138 2.12 Concluding Remarks 140 2.13 Historical Perspective and References 141 Case Studies with Exercises by Robert P.Colwell 142 Chapter 3 Limits on Instruction-Level Parallelism 3.1 Introduction 154 3.2 Studies of the Limitations of ILP 154 3.3 Limitations on ILP for Realizable Processors 165 3.4 Crosscutting Issues:Hardware versus Software Speculation 170 3.5 Multithreading: Using ILP Support to Exploit Thread-Level Parallelism 172 3.6 Putting It All Together:Performance and Efciency in Advanced Multiple-Issue Processors 179 3.7 Fallacies and Pitfalls 183 3.8 Concluding Remarks 184 3.9 Historical Perspective and References 185 Case Study with Exercises by Wen-mei W.Hwu and John W.Sias 185 Chapter4 Multiprocessors and Thread-Level Parallelism 4.1 Introduction 196 4.2 Symmetric Shared-Memory Architectures 205 4.3 Performance of Symmetric Shared-Memory Multiprocessors 218 4.4 Distributed Shared Memory and Directory-Based Coherence 230 4.5 Synchronization:The Basics 237 4.6 Models of Memory Consistency:An Introduction 243 4.7 Crosscutting Issues 246 4.8 Putting It All Together:The Sun T1 Multiprocessor 249 4.9 Fallacies and Pitfalls 257 4.10 Concluding Remarks 262 4.11 Historical Perspective and References 264 Case Studies with Exercises by David A.Wood 264 Chapter 5 Memory Hierarchy Design 5.1 Introduction 288 5.2 Eleven Advanced Optimizations of Cache Performance 293 5.3 Memory Technology and Optimizations 310 13. Contents I xiii 5.4 Protection:Virtual Memory and Virtual Machines 315 5.5 Crosscutting Issues: The Design of Memory Hierarchies 324 5.6 Putting It All Together:AMD Opteron Memory Hierarchy 326 5.7 Fallacies and Pitfalls 335 5.8 Concluding Remarks 341 5.9 Historical Perspective and References 342 Case Studies with Exercises by Norman P.Jouppi 342 Chapter6 Storage Systems 6.1 Introduction 358 6.2 Advanced Topics in Disk Storage 358 6.3 Denition and Examples of Real Faults and Failures 366 6.4 I/O Performance,Reliability Measures,and Benchmarks 371 6.5 A Little Queuing Theory 379 6.6 Crosscutting Issues 390 6.7 Designing and Evaluating an I/O SystemThe Internet Archive Cluster 392 6.8 Putting It All Together:NetApp FAS6000 Filer 397 6.9 Fallacies and Pitfalls 399 6.10 Concluding Remarks 403 6.11 Historical Perspective and References 404 Case Studies with Exercises by Andrea C.Arpaci-Dusseau and Remzi H.Arpaci-Dusseau 404 Appendix A Pipelining: Basic and Intermediate Concepts A.1 Introduction A-2 A.2 The Major Hurdle of PipeliningPipeline Hazards A-11 A.3 How Is Pipelining Implemented? A-26 A.4 What Makes Pipelining Hard to Implement? A-37 A.5 Extending the MIPS Pipeline to Handle Multicycle Operations A-47 A.6 Putting It All Together:The MIPS R4000 Pipeline A-56 A.7 Crosscutting Issues A-65 A.8 Fallacies and Pitfalls A-75 A.9 Concluding Remarks A-76 A.10 Historical Perspective and References A-77 AppendixB Instruction Set Principles and Examples B.1 Introduction B-2 B.2 Classifying Instruction Set Architectures B-3 B.3 Memory Addressing B-7 B.4 Type and Size of Operands B-13 B.5 Operations in the Instruction Set B-14 14. xiv I Contents B.6 Instructions for Control Flow B-16 B.7 Encoding an Instruction Set B-21 B.8 Crosscutting Issues:The Role of Compilers B-24 B.9 Putting It All Together:The MIPS Architecture B-32 B.10 Fallacies and Pitfalls B-39 B.11 Concluding Remarks B-45 B.12 Historical Perspective and References B-47 Appendix C Review of Memory Hierarchy C.1 Introduction C-2 C.2 Cache Performance C-15 C.3 Six Basic Cache Optimizations C-22 C.4 Virtual Memory C-38 C.5 Protection and Examples of Virtual Memory C-47 C.6 Fallacies and Pitfalls C-56 C.7 Concluding Remarks C-57 C.8 Historical Perspective and References C-58 Companion CD Appendices Appendix D Embedded Systems Updated byThomas M.Conte Appendix E Interconnection Networks Revised byTimothy M.Pinkston and Jos Duato Appendix F Vector Processors Revised by Krste Asanovic Appendix G Hardware and Software for VLIW and EPIC Appendix H Large-Scale Multiprocessors and Scientic Applications Appendix I Computer Arithmetic by David Goldberg Appendix J Survey of Instruction Set Architectures Appendix K Historical Perspectives and References Online Appendix (textbooks.elsevier.com/0123704901) Appendix L Solutions to Case Study Exercises References R-1 Index I-1 15. xv Why We Wrote This Book Through four editions of this book, our goal has been to describe the basic principles underlying what will be tomorrows technological developments. Our excitement about the opportunities in computer architecture has not abated, and we echo what we said about the eld in the rst edition: It is not a dreary science of paper machines that will never work. No! Its a discipline of keen intellectual interest, requiring the balance of marketplace forces to cost-performance-power, leading to glorious failures and some notable successes. Our primary objective in writing our rst book was to change the way people learn and think about computer architecture. We feel this goal is still valid and important. The eld is changing daily and must be studied with real examples and measurements on real computers, rather than simply as a collection of deni- tions and designs that will never need to be realized. We offer an enthusiastic welcome to anyone who came along with us in the past, as well as to those who are joining us now. Either way, we can promise the same quantitative approach to, and analysis of, real systems. As with earlier versions, we have strived to produce a new edition that will continue to be as relevant for professional engineers and architects as it is for those involved in advanced computer architecture and design courses. As much as its predecessors, this edition aims to demystify computer architecture through an emphasis on cost-performance-power trade-offs and good engineering design. We believe that the eld has continued to mature and move toward the rigorous quantitative foundation of long-established scientic and engineering disciplines. This Edition The fourth edition of Computer Architecture: A Quantitative Approach may be the most signicant since the rst edition. Shortly before we started this revision, Intel announced that it was joining IBM and Sun in relying on multiple processors or cores per chip for high-performance designs. As the rst gure in the book documents, after 16 years of doubling performance every 18 months, sin- Preface 16. xvi I Preface gle-processor performance improvement has dropped to modest annual improvements. This fork in the computer architecture road means that for the rst time in history, no one is building a much faster sequential processor. If you want your program to run signicantly faster, say, to justify the addition of new features, youre going to have to parallelize your program. Hence, after three editions focused primarily on higher performance by exploiting instruction-level parallelism (ILP), an equal focus of this edition is thread-level parallelism (TLP) and data-level parallelism (DLP). While earlier editions had material on TLP and DLP in big multiprocessor servers, now TLP and DLP are relevant for single-chip multicores. This historic shift led us to change the order of the chapters: the chapter on multiple processors was the sixth chapter in the last edition, but is now the fourth chapter of this edition. The changing technology has also motivated us to move some of the content from later chapters into the rst chapter. Because technologists predict much higher hard and soft error rates as the industry moves to semiconductor processes with feature sizes 65 nm or smaller, we decided to move the basics of dependability from Chapter 7 in the third edition into Chapter 1. As power has become the dominant factor in determining how much you can place on a chip, we also beefed up the coverage of power in Chapter 1. Of course, the content and examples in all chapters were updated, as we discuss below. In addition to technological sea changes that have shifted the contents of this edition, we have taken a new approach to the exercises in this edition. It is sur- prisingly difcult and time-consuming to create interesting, accurate, and unam- biguous exercises that evenly test the material throughout a chapter. Alas, the Web has reduced the half-life of exercises to a few months. Rather than working out an assignment, a student can search the Web to nd answers not long after a book is published. Hence, a tremendous amount of hard work quickly becomes unusable, and instructors are denied the opportunity to test what students have learned. To help mitigate this problem, in this edition we are trying two new ideas. First, we recruited experts from academia and industry on each topic to write the exercises. This means some of the best people in each eld are helping us to create interesting ways to explore the key concepts in each chapter and test the readers understanding of that material. Second, each group of exercises is orga- nized around a set of case studies. Our hope is that the quantitative example in each case study will remain interesting over the years, robust and detailed enough to allow instructors the opportunity to easily create their own new exercises, should they choose to do so. Key, however, is that each year we will continue to release new exercise sets for each of the case studies. These new exercises will have critical changes in some parameters so that answers to old exercises will no longer apply. Another signicant change is that we followed the lead of the third edition of Computer Organization and Design (COD) by slimming the text to include the material that almost all readers will want to see and moving the appendices that 17. Preface I xvii some will see as optional or as reference material onto a companion CD. There were many reasons for this change: 1. Students complained about the size of the book, which had expanded from 594 pages in the chapters plus 160 pages of appendices in the rst edition to 760 chapter pages plus 223 appendix pages in the second edition and then to 883 chapter pages plus 209 pages in the paper appendices and 245 pages in online appendices. At this rate, the fourth edition would have exceeded 1500 pages (both on paper and online)! 2. Similarly, instructors were concerned about having too much material to cover in a single course. 3. As was the case for COD, by including a CD with material moved out of the text, readers could have quick access to all the material, regardless of their ability to access Elseviers Web site. Hence, the current editions appendices will always be available to the reader even after future editions appear. 4. This exibility allowed us to move review material on pipelining, instruction sets, and memory hierarchy from the chapters and into Appendices A, B, and C. The advantage to instructors and readers is that they can go over the review material much more quickly and then spend more time on the advanced topics in Chapters 2, 3, and 5. It also allowed us to move the discussion of some topics that are important but are not core course topics into appendices on the CD. Result: the material is available, but the printed book is shorter. In this edition we have 6 chapters, none of which is longer than 80 pages, while in the last edition we had 8 chapters, with the longest chapter weighing in at 127 pages. 5. This package of a slimmer core print text plus a CD is far less expensive to manufacture than the previous editions, allowing our publisher to signicantly lower the list price of the book. With this pricing scheme, there is no need for a separate international student edition for European readers. Yet another major change from the last edition is that we have moved the embedded material introduced in the third edition into its own appendix, Appen- dix D. We felt that the embedded material didnt always t with the quantitative evaluation of the rest of the material, plus it extended the length of many chapters that were already running long. We believe there are also pedagogic advantages in having all the embedded information in a single appendix. This edition continues the tradition of using real-world examples to demonstrate the ideas, and the Putting It All Together sections are brand new; in fact, some were announced after our book was sent to the printer. The Putting It All Together sections of this edition include the pipeline organizations and memory hierarchies of the Intel Pentium 4 and AMD Opteron; the Sun T1 (Niagara) 8- processor, 32-thread microprocessor; the latest NetApp Filer; the Internet Archive cluster; and the IBM Blue Gene/L massively parallel processor. 18. xviii I Preface Topic Selection and Organization As before, we have taken a conservative approach to topic selection, for there are many more interesting ideas in the eld than can reasonably be covered in a treat- ment of basic principles. We have steered away from a comprehensive survey of every architecture a reader might encounter. Instead, our presentation focuses on core concepts likely to be found in any new machine. The key criterion remains that of selecting ideas that have been examined and utilized successfully enough to permit their discussion in quantitative terms. Our intent has always been to focus on material that is not available in equiva- lent form from other sources, so we continue to emphasize advanced content wherever possible. Indeed, there are several systems here whose descriptions cannot be found in the literature. (Readers interested strictly in a more basic introduction to computer architecture should read Computer Organization and Design: The Hardware/Software Interface, third edition.) An Overview of the Content Chapter 1 has been beefed up in this edition. It includes formulas for static power, dynamic power, integrated circuit costs, reliability, and availability. We go into more depth than prior editions on the use of the geometric mean and the geometric standard deviation to capture the variability of the mean. Our hope is that these topics can be used through the rest of the book. In addition to the classic quantitative principles of computer design and performance measurement, the benchmark section has been upgraded to use the new SPEC2006 suite. Our view is that the instruction set architecture is playing less of a role today than in 1990, so we moved this material to Appendix B. It still uses the MIPS64 architecture. For fans of ISAs, Appendix J covers 10 RISC architectures, the 80x86, the DEC VAX, and the IBM 360/370. Chapters 2 and 3 cover the exploitation of instruction-level parallelism in high-performance processors, including superscalar execution, branch prediction, speculation, dynamic scheduling, and the relevant compiler technology. As mentioned earlier, Appendix A is a review of pipelining in case you need it. Chapter 3 surveys the limits of ILP. New to this edition is a quantitative evaluation of multithreading. Chapter 3 also includes a head-to-head comparison of the AMD Ath- lon, Intel Pentium 4, Intel Itanium 2, and IBM Power5, each of which has made separate bets on exploiting ILP and TLP. While the last edition contained a great deal on Itanium, we moved much of this material to Appendix G, indicating our view that this architecture has not lived up to the early claims. Given the switch in the eld from exploiting only ILP to an equal focus on thread- and data-level parallelism, we moved multiprocessor systems up to Chap- ter 4, which focuses on shared-memory architectures. The chapter begins with the performance of such an architecture. It then explores symmetric and distributed memory architectures, examining both organizational principles and performance. Topics in synchronization and memory consistency models are 19. Preface I xix next. The example is the Sun T1 (Niagara), a radical design for a commercial product. It reverted to a single-instruction issue, 6-stage pipeline microarchitecture. It put 8 of these on a single chip, and each supports 4 threads. Hence, software sees 32 threads on this single, low-power chip. As mentioned earlier, Appendix C contains an introductory review of cache principles, which is available in case you need it. This shift allows Chapter 5 to start with 11 advanced optimizations of caches. The chapter includes a new section on virtual machines, which offers advantages in protection, software management, and hardware management. The example is the AMD Opteron, giving both its cache hierarchy and the virtual memory scheme for its recently expanded 64-bit addresses. Chapter 6, Storage Systems, has an expanded discussion of reliability and availability, a tutorial on RAID with a description of RAID 6 schemes, and rarely found failure statistics of real systems. It continues to provide an introduction to queuing theory and I/O performance benchmarks. Rather than go through a series of steps to build a hypothetical cluster as in the last edition, we evaluate the cost, performance, and reliability of a real cluster: the Internet Archive. The Putting It All Together example is the NetApp FAS6000 ler, which is based on the AMD Opteron microprocessor. This brings us to Appendices A through L. As mentioned earlier, Appendices A and C are tutorials on basic pipelining and caching concepts. Readers relatively new to pipelining should read Appendix A before Chapters 2 and 3, and those new to caching should read Appendix C before Chapter 5. Appendix B covers principles of ISAs, including MIPS64, and Appendix J describes 64-bit versions of Alpha, MIPS, PowerPC, and SPARC and their multi- media extensions. It also includes some classic architectures (80x86, VAX, and IBM 360/370) and popular embedded instruction sets (ARM, Thumb, SuperH, MIPS16, and Mitsubishi M32R). Appendix G is related, in that it covers architectures and compilers for VLIW ISAs. Appendix D, updated by Thomas M. Conte, consolidates the embedded material in one place. Appendix E, on networks, has been extensively revised by Timothy M. Pink- ston and Jos Duato. Appendix F, updated by Krste Asanovic, includes a description of vector processors. We think these two appendices are some of the best material we know of on each topic. Appendix H describes parallel processing applications and coherence proto- cols for larger-scale, shared-memory multiprocessing. Appendix I, by David Goldberg, describes computer arithmetic. Appendix K collects the Historical Perspective and References from each chapter of the third edition into a single appendix. It attempts to give proper credit for the ideas in each chapter and a sense of the history surrounding the inventions. We like to think of this as presenting the human drama of computer design. It also supplies references that the student of architecture may want to pursue. If you have time, we recommend reading some of the classic papers in the eld that are mentioned in these sections. It is both enjoyable and educational 20. xx I Preface to hear the ideas directly from the creators. Historical Perspective was one of the most popular sections of prior editions. Appendix L (available at textbooks.elsevier.com/0123704901) contains solutions to the case study exercises in the book. Navigating the Text There is no single best order in which to approach these chapters and appendices, except that all readers should start with Chapter 1. If you dont want to read everything, here are some suggested sequences: I ILP: Appendix A, Chapters 2 and 3, and Appendices F and G I Memory Hierarchy: Appendix C and Chapters 5 and 6 I Thread-and Data-Level Parallelism: Chapter 4, Appendix H, and Appendix E I ISA: Appendices B and J Appendix D can be read at any time, but it might work best if read after the ISA and cache sequences. Appendix I can be read whenever arithmetic moves you. Chapter Structure The material we have selected has been stretched upon a consistent framework that is followed in each chapter. We start by explaining the ideas of a chapter. These ideas are followed by a Crosscutting Issues section, a feature that shows how the ideas covered in one chapter interact with those given in other chapters. This is followed by a Putting It All Together section that ties these ideas together by showing how they are used in a real machine. Next in the sequence is Fallacies and Pitfalls, which lets readers learn from the mistakes of others. We show examples of common misunderstandings and architectural traps that are difcult to avoid even when you know they are lying in wait for you. The Fallacies and Pitfalls sections is one of the most popular sections of the book. Each chapter ends with a Concluding Remarks section. Case Studies with Exercises Each chapter ends with case studies and accompanying exercises. Authored by experts in industry and academia, the case studies explore key chapter concepts and verify understanding through increasingly challenging exercises. Instructors should nd the case studies sufciently detailed and robust to allow them to create their own additional exercises. Brackets for each exercise () indicate the text sections of primary relevance to completing the exercise. We hope this helps readers to avoid exercises for which they havent read the corresponding section, in addition to providing the source for review. Note that we provide solutions to the case study 21. Preface I xxi exercises in Appendix L. Exercises are rated, to give the reader a sense of the amount of time required to complete an exercise: [10] Less than 5 minutes (to read and understand) [15] 515 minutes for a full answer [20] 1520 minutes for a full answer [25] 1 hour for a full written answer [30] Short programming project: less than 1 full day of programming [40] Signicant programming project: 2 weeks of elapsed time [Discussion] Topic for discussion with others A second set of alternative case study exercises are available for instructors who register at textbooks.elsevier.com/0123704901. This second set will be revised every summer, so that early every fall, instructors can download a new set of exercises and solutions to accompany the case studies in the book. Supplemental Materials The accompanying CD contains a variety of resources, including the following: I Reference appendicessome guest authored by subject expertscovering a range of advanced topics I Historical Perspectives material that explores the development of the key ideas presented in each of the chapters in the text I Search engine for both the main text and the CD-only content Additional resources are available at textbooks.elsevier.com/0123704901. The instructor site (accessible to adopters who register at textbooks.elsevier.com) includes: I Alternative case study exercises with solutions (updated yearly) I Instructor slides in PowerPoint I Figures from the book in JPEG and PPT formats The companion site (accessible to all readers) includes: I Solutions to the case study exercises in the text I Links to related material on the Web I List of errata New materials and links to other resources available on the Web will be added on a regular basis. 22. xxii I Preface Helping Improve This Book Finally, it is possible to make money while reading this book. (Talk about cost- performance!) If you read the Acknowledgments that follow, you will see that we went to great lengths to correct mistakes. Since a book goes through many print- ings, we have the opportunity to make even more corrections. If you uncover any remaining resilient bugs, please contact the publisher by electronic mail ([email protected]). The rst reader to report an error with a x that we incorporate in a future printing will be rewarded with a $1.00 bounty. Please check the errata sheet on the home page (textbooks.elsevier.com/0123704901) to see if the bug has already been reported. We process the bugs and send the checks about once a year or so, so please be patient. We welcome general comments to the text and invite you to send them to a separate email address at [email protected]. Concluding Remarks Once again this book is a true co-authorship, with each of us writing half the chapters and an equal share of the appendices. We cant imagine how long it would have taken without someone else doing half the work, offering inspiration when the task seemed hopeless, providing the key insight to explain a difcult concept, supplying reviews over the weekend of chapters, and commiserating when the weight of our other obligations made it hard to pick up the pen. (These obligations have escalated exponentially with the number of editions, as one of us was President of Stanford and the other was President of the Association for Computing Machinery.) Thus, once again we share equally the blame for what you are about to read. John Hennessy I David Patterson 23. xxiii Although this is only the fourth edition of this book, we have actually created nine different versions of the text: three versions of the rst edition (alpha, beta, and nal) and two versions of the second, third, and fourth editions (beta and nal). Along the way, we have received help from hundreds of reviewers and users. Each of these people has helped make this book better. Thus, we have chosen to list all of the people who have made contributions to some version of this book. Contributors to the Fourth Edition Like prior editions, this is a community effort that involves scores of volunteers. Without their help, this edition would not be nearly as polished. Reviewers Krste Asanovic, Massachusetts Institute of Technology; Mark Brehob, University of Michigan; Sudhanva Gurumurthi, University of Virginia; Mark D. Hill, Uni- versity of WisconsinMadison; Wen-mei Hwu, University of Illinois at Urbana Champaign; David Kaeli, Northeastern University; Ramadass Nagarajan, Univer- sity of Texas at Austin; Karthikeyan Sankaralingam, Univeristy of Texas at Aus- tin; Mark Smotherman, Clemson University; Gurindar Sohi, University of WisconsinMadison; Shyamkumar Thoziyoor, University of Notre Dame, Indi- ana; Dan Upton, University of Virginia; Sotirios G. Ziavras, New Jersey Institute of Technology Focus Group Krste Asanovic, Massachusetts Institute of Technology; Jos Duato, Universitat Politcnica de Valncia and Simula; Antonio Gonzlez, Intel and Universitat Politcnica de Catalunya; Mark D. Hill, University of WisconsinMadison; Lev G. Kirischian, Ryerson University; Timothy M. Pinkston, University of Southern California Acknowledgments 24. xxiv I Acknowledgments Appendices Krste Asanovic, Massachusetts Institute of Technology (Appendix F); Thomas M. Conte, North Carolina State University (Appendix D); Jos Duato, Universi- tat Politcnica de Valncia and Simula (Appendix E); David Goldberg, Xerox PARC (Appendix I); Timothy M. Pinkston, University of Southern California (Appendix E) Case Studies with Exercises Andrea C. Arpaci-Dusseau, University of WisconsinMadison (Chapter 6); Remzi H. Arpaci-Dusseau, University of WisconsinMadison (Chapter 6); Robert P. Col- well, R&E Colwell & Assoc., Inc. (Chapter 2); Diana Franklin, California Poly- technic State University, San Luis Obispo (Chapter 1); Wen-mei W. Hwu, University of Illinois at UrbanaChampaign (Chapter 3); Norman P. Jouppi, HP Labs (Chapter 5); John W. Sias, University of Illinois at UrbanaChampaign (Chapter 3); David A. Wood, University of WisconsinMadison (Chapter 4) Additional Material John Mashey (geometric means and standard deviations in Chapter 1); Chenming Hu, University of California, Berkeley (wafer costs and yield parameters in Chapter 1); Bill Brantley and Dan Mudgett, AMD (Opteron memory hierarchy evaluation in Chapter 5); Mendel Rosenblum, Stanford and VMware (virtual machines in Chapter 5); Aravind Menon, EPFL Switzerland (Xen measurements in Chapter 5); Bruce Baumgart and Brewster Kahle, Internet Archive (IA cluster in Chapter 6); David Ford, Steve Kleiman, and Steve Miller, Network Appliances (FX6000 information in Chapter 6); Alexander Thomasian, Rutgers (queueing theory in Chapter 6) Finally, a special thanks once again to Mark Smotherman of Clemson Univer- sity, who gave a nal technical reading of our manuscript. Mark found numerous bugs and ambiguities, and the book is much cleaner as a result. This book could not have been published without a publisher, of course. We wish to thank all the Morgan Kaufmann/Elsevier staff for their efforts and support. For this fourth edition, we particularly want to thank Kimberlee Honjo who coordinated surveys, focus groups, manuscript reviews and appendices, and Nate McFadden, who coordinated the development and review of the case studies. Our warmest thanks to our editor, Denise Penrose, for her leadership in our continu- ing writing saga. We must also thank our university staff, Margaret Rowland and Cecilia Pracher, for countless express mailings, as well as for holding down the fort at Stanford and Berkeley while we worked on the book. Our nal thanks go to our wives for their suffering through increasingly early mornings of reading, thinking, and writing. 25. Acknowledgments I xxv Contributors to Previous Editions Reviewers George Adams, Purdue University; Sarita Adve, University of Illinois at Urbana Champaign; Jim Archibald, Brigham Young University; Krste Asanovic, Massa- chusetts Institute of Technology; Jean-Loup Baer, University of Washington; Paul Barr, Northeastern University; Rajendra V. Boppana, University of Texas, San Antonio; Doug Burger, University of Texas, Austin; John Burger, SGI; Michael Butler; Thomas Casavant; Rohit Chandra; Peter Chen, University of Michigan; the classes at SUNY Stony Brook, Carnegie Mellon, Stanford, Clem- son, and Wisconsin; Tim Coe, Vitesse Semiconductor; Bob Colwell, Intel; David Cummings; Bill Dally; David Douglas; Anthony Duben, Southeast Missouri State University; Susan Eggers, University of Washington; Joel Emer; Barry Fagin, Dartmouth; Joel Ferguson, University of California, Santa Cruz; Carl Fey- nman; David Filo; Josh Fisher, Hewlett-Packard Laboratories; Rob Fowler, DIKU; Mark Franklin, Washington University (St. Louis); Kourosh Gharachor- loo; Nikolas Gloy, Harvard University; David Goldberg, Xerox Palo Alto Research Center; James Goodman, University of WisconsinMadison; David Harris, Harvey Mudd College; John Heinlein; Mark Heinrich, Stanford; Daniel Helman, University of California, Santa Cruz; Mark Hill, University of Wiscon- sinMadison; Martin Hopkins, IBM; Jerry Huck, Hewlett-Packard Laboratories; Mary Jane Irwin, Pennsylvania State University; Truman Joe; Norm Jouppi; David Kaeli, Northeastern University; Roger Kieckhafer, University of Nebraska; Earl Killian; Allan Knies, Purdue University; Don Knuth; Jeff Kuskin, Stanford; James R. Larus, Microsoft Research; Corinna Lee, University of Tor- onto; Hank Levy; Kai Li, Princeton University; Lori Liebrock, University of Alaska, Fairbanks; Mikko Lipasti, University of WisconsinMadison; Gyula A. Mago, University of North Carolina, Chapel Hill; Bryan Martin; Norman Mat- loff; David Meyer; William Michalson, Worcester Polytechnic Institute; James Mooney; Trevor Mudge, University of Michigan; David Nagle, Carnegie Mellon University; Todd Narter; Victor Nelson; Vojin Oklobdzija, University of Califor- nia, Berkeley; Kunle Olukotun, Stanford University; Bob Owens, Pennsylvania State University; Greg Papadapoulous, Sun; Joseph Pfeiffer; Keshav Pingali, Cornell University; Bruno Preiss, University of Waterloo; Steven Przybylski; Jim Quinlan; Andras Radics; Kishore Ramachandran, Georgia Institute of Technol- ogy; Joseph Rameh, University of Texas, Austin; Anthony Reeves, Cornell Uni- versity; Richard Reid, Michigan State University; Steve Reinhardt, University of Michigan; David Rennels, University of California, Los Angeles; Arnold L. Rosenberg, University of Massachusetts, Amherst; Kaushik Roy, Purdue Univer- sity; Emilio Salgueiro, Unysis; Peter Schnorf; Margo Seltzer; Behrooz Shirazi, Southern Methodist University; Daniel Siewiorek, Carnegie Mellon University; J. P. Singh, Princeton; Ashok Singhal; Jim Smith, University of Wisconsin Madison; Mike Smith, Harvard University; Mark Smotherman, Clemson Univer- sity; Guri Sohi, University of WisconsinMadison; Arun Somani, University of 26. xxvi I Acknowledgments Washington; Gene Tagliarin, Clemson University; Evan Tick, University of Ore- gon; Akhilesh Tyagi, University of North Carolina, Chapel Hill; Mateo Valero, Universidad Politcnica de Catalua, Barcelona; Anujan Varma, University of California, Santa Cruz; Thorsten von Eicken, Cornell University; Hank Walker, Texas A&M; Roy Want, Xerox Palo Alto Research Center; David Weaver, Sun; Shlomo Weiss, Tel Aviv University; David Wells; Mike Westall, Clemson Univer- sity; Maurice Wilkes; Eric Williams; Thomas Willis, Purdue University; Malcolm Wing; Larry Wittie, SUNY Stony Brook; Ellen Witte Zegura, Georgia Institute of Technology Appendices The vector appendix was revised by Krste Asanovic of the Massachusetts Insti- tute of Technology. The oating-point appendix was written originally by David Goldberg of Xerox PARC. Exercises George Adams, Purdue University; Todd M. Bezenek, University of Wisconsin Madison (in remembrance of his grandmother Ethel Eshom); Susan Eggers; Anoop Gupta; David Hayes; Mark Hill; Allan Knies; Ethan L. Miller, University of California, Santa Cruz; Parthasarathy Ranganathan, Compaq Western Research Laboratory; Brandon Schwartz, University of WisconsinMadison; Michael Scott; Dan Siewiorek; Mike Smith; Mark Smotherman; Evan Tick; Tho- mas Willis. SpecialThanks Duane Adams, Defense Advanced Research Projects Agency; Tom Adams; Sarita Adve, University of Illinois at UrbanaChampaign; Anant Agarwal; Dave Albo- nesi, University of Rochester; Mitch Alsup; Howard Alt; Dave Anderson; Peter Ashenden; David Bailey; Bill Bandy, Defense Advanced Research Projects Agency; L. Barroso, Compaqs Western Research Lab; Andy Bechtolsheim; C. Gordon Bell; Fred Berkowitz; John Best, IBM; Dileep Bhandarkar; Jeff Bier, BDTI; Mark Birman; David Black; David Boggs; Jim Brady; Forrest Brewer; Aaron Brown, University of California, Berkeley; E. Bugnion, Compaqs West- ern Research Lab; Alper Buyuktosunoglu, University of Rochester; Mark Cal- laghan; Jason F. Cantin; Paul Carrick; Chen-Chung Chang; Lei Chen, University of Rochester; Pete Chen; Nhan Chu; Doug Clark, Princeton University; Bob Cmelik; John Crawford; Zarka Cvetanovic; Mike Dahlin, University of Texas, Austin; Merrick Darley; the staff of the DEC Western Research Laboratory; John DeRosa; Lloyd Dickman; J. Ding; Susan Eggers, University of Washington; Wael El-Essawy, University of Rochester; Patty Enriquez, Mills; Milos Ercegovac; Robert Garner; K. Gharachorloo, Compaqs Western Research Lab; Garth Gib- son; Ronald Greenberg; Ben Hao; John Henning, Compaq; Mark Hill, University 27. Acknowledgments I xxvii of WisconsinMadison; Danny Hillis; David Hodges; Urs Hoelzle, Google; David Hough; Ed Hudson; Chris Hughes, University of Illinois at Urbana Champaign; Mark Johnson; Lewis Jordan; Norm Jouppi; William Kahan; Randy Katz; Ed Kelly; Richard Kessler; Les Kohn; John Kowaleski, Compaq Computer Corp; Dan Lambright; Gary Lauterbach, Sun Microsystems; Corinna Lee; Ruby Lee; Don Lewine; Chao-Huang Lin; Paul Losleben, Defense Advanced Research Projects Agency; Yung-Hsiang Lu; Bob Lucas, Defense Advanced Research Projects Agency; Ken Lutz; Alan Mainwaring, Intel Berkeley Research Labs; Al Marston; Rich Martin, Rutgers; John Mashey; Luke McDowell; Sebastian Mirolo, Trimedia Corporation; Ravi Murthy; Biswadeep Nag; Lisa Noordergraaf, Sun Microsystems; Bob Parker, Defense Advanced Research Projects Agency; Vern Paxson, Center for Internet Research; Lawrence Prince; Steven Przybylski; Mark Pullen, Defense Advanced Research Projects Agency; Chris Rowen; Marg- aret Rowland; Greg Semeraro, University of Rochester; Bill Shannon; Behrooz Shirazi; Robert Shomler; Jim Slager; Mark Smotherman, Clemson University; the SMT research group at the University of Washington; Steve Squires, Defense Advanced Research Projects Agency; Ajay Sreekanth; Darren Staples; Charles Stapper; Jorge Stol; Peter Stoll; the students at Stanford and Berkeley who endured our rst attempts at creating this book; Bob Supnik; Steve Swanson; Paul Taysom; Shreekant Thakkar; Alexander Thomasian, New Jersey Institute of Technology; John Toole, Defense Advanced Research Projects Agency; Kees A. Vissers, Trimedia Corporation; Willa Walker; David Weaver; Ric Wheeler, EMC; Maurice Wilkes; Richard Zimmerman. John Hennessy I David Patterson 28. 1.1 Introduction 2 1.2 Classes of Computers 4 1.3 Dening Computer Architecture 8 1.4 Trends in Technology 14 1.5 Trends in Power in Integrated Circuits 17 1.6 Trends in Cost 19 1.7 Dependability 25 1.8 Measuring,Reporting,and Summarizing Performance 28 1.9 Quantitative Principles of Computer Design 37 1.10 Putting It All Together:Performance and Price-Performance 44 1.11 Fallacies and Pitfalls 48 1.12 Concluding Remarks 52 1.13 Historical Perspectives and References 54 Case Studies with Exercises by Diana Franklin 55 29. 1 Fundamentals of Computer Design And now for something completely different. Monty Pythons Flying Circus 30. 2 I Chapter One Fundamentals of Computer Design Computer technology has made incredible progress in the roughly 60 years since the rst general-purpose electronic computer was created. Today, less than $500 will purchase a personal computer that has more performance, more main memory, and more disk storage than a computer bought in 1985 for 1 million dollars. This rapid improvement has come both from advances in the technology used to build computers and from innovation in computer design. Although technological improvements have been fairly steady, progress aris- ing from better computer architectures has been much less consistent. During the rst 25 years of electronic computers, both forces made a major contribution, delivering performance improvement of about 25% per year. The late 1970s saw the emergence of the microprocessor. The ability of the microprocessor to ride the improvements in integrated circuit technology led to a higher rate of improve- mentroughly 35% growth per year in performance. This growth rate, combined with the cost advantages of a mass-produced microprocessor, led to an increasing fraction of the computer business being based on microprocessors. In addition, two signicant changes in the computer marketplace made it easier than ever before to be commercially successful with a new architecture. First, the virtual elimination of assembly language programming reduced the need for object-code compatibility. Second, the creation of standardized, vendor-independent operating systems, such as UNIX and its clone, Linux, lowered the cost and risk of bringing out a new architecture. These changes made it possible to develop successfully a new set of architectures with simpler instructions, called RISC (Reduced Instruction Set Computer) architectures, in the early 1980s. The RISC-based machines focused the attention of designers on two critical performance techniques, the exploitation of instruction- level parallelism (initially through pipelining and later through multiple instruction issue) and the use of caches (initially in simple forms and later using more sophisti- cated organizations and optimizations). The RISC-based computers raised the performance bar, forcing prior architectures to keep up or disappear. The Digital Equipment Vax could not, and so it was replaced by a RISC architecture. Intel rose to the challenge, primarily by translating x86 (or IA-32) instructions into RISC-like instructions internally, allowing it to adopt many of the innovations rst pioneered in the RISC designs. As transistor counts soared in the late 1990s, the hardware overhead of translating the more complex x86 architecture became negligible. Figure 1.1 shows that the combination of architectural and organizational enhancements led to 16 years of sustained growth in performance at an annual rate of over 50%a rate that is unprecedented in the computer industry. The effect of this dramatic growth rate in the 20th century has been twofold. First, it has signicantly enhanced the capability available to computer users. For many applications, the highest-performance microprocessors of today outper- form the supercomputer of less than 10 years ago. 1.1 Introduction 31. 1.1 Introduction I 3 Second, this dramatic rate of improvement has led to the dominance of microprocessor-based computers across the entire range of the computer design. PCs and Workstations have emerged as major products in the computer industry. Minicomputers, which were traditionally made from off-the-shelf logic or from gate arrays, have been replaced by servers made using microprocessors. Main- frames have been almost replaced with multiprocessors consisting of small numbers of off-the-shelf microprocessors. Even high-end supercomputers are being built with collections of microprocessors. These innovations led to a renaissance in computer design, which emphasized both architectural innovation and efcient use of technology improvements. This rate of growth has compounded so that by 2002, high-performance microprocessors are about seven times faster than what would have been obtained by relying solely on technology, including improved circuit design. Figure 1.1 Growth in processor performance since the mid-1980s. This chart plots performance relative to the VAX 11/780 as measured by the SPECint benchmarks (see Section 1.8). Prior to the mid-1980s, processor performance growth was largely technology driven and averaged about 25% per year. The increase in growth to about 52% since then is attributable to more advanced architectural and organizational ideas.By 2002,this growth led to a difference in performance of about a factor of seven. Performance for oating-point-oriented calculations has increased even faster. Since 2002, the limits of power, available instruction-level parallelism, and long memory latency have slowed uniprocessor performance recently, to about 20% per year. Since SPEC has changed over the years,performance of newer machines is estimated by a scaling factor that relates the performance for two different versions of SPEC (e.g.,SPEC92,SPEC95,and SPEC2000). Performance(vs.VAX-11/780) 10,000 1000 100 10 1978 0 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 1779 Intel Pentium III, 1.0 GHz 2584 AMD Athlon, 1.6 GHz Intel Pentium 4,3.0 GHz 4195 AMD Opteron, 2.2 GHz 5364 5764 Intel Xeon, 3.6 GHz 64-bit Intel Xeon, 3.6 GHz 6505 1267 Alpha 21264A, 0.7 GHz 993 Alpha 21264, 0.6 GHz 649 Alpha 21164, 0.6 GHz 481 Alpha 21164, 0.5 GHz 280 Alpha 21164, 0.3 GHz 183 Alpha 21064A, 0.3 GHz 117PowerPC 604, 0.1GHz 80 Alpha 21064, 0.2 GHz 51 HP PA-RISC, 0.05 GHz 24 IBM RS6000/540 18 MIPS M2000 13MIPS M/120 9Sun-4/260 5 VAX 8700 1.5, VAX-11/785 25%/year 52%/year 20% VAX-11/780 32. 4 I Chapter One Fundamentals of Computer Design However, Figure 1.1 also shows that this 16-year renaissance is over. Since 2002, processor performance improvement has dropped to about 20% per year due to the triple hurdles of maximum power dissipation of air-cooled chips, little instruction-level parallelism left to exploit efciently, and almost unchanged memory latency. Indeed, in 2004 Intel canceled its high-performance uniprocessor projects and joined IBM and Sun in declaring that the road to higher performance would be via multiple processors per chip rather than via faster uniprocessors. This signals a historic switch from relying solely on instruction- level parallelism (ILP), the primary focus of the rst three editions of this book, to thread-level parallelism (TLP) and data-level parallelism (DLP), which are featured in this edition. Whereas the compiler and hardware conspire to exploit ILP implicitly without the programmers attention, TLP and DLP are explicitly parallel, requiring the programmer to write parallel code to gain performance. This text is about the architectural ideas and accompanying compiler improvements that made the incredible growth rate possible in the last century, the reasons for the dramatic change, and the challenges and initial promising approaches to architectural ideas and compilers for the 21st century. At the core is a quantitative approach to computer design and analysis that uses empirical observations of programs, experimentation, and simulation as its tools. It is this style and approach to computer design that is reected in this text. This book was written not only to explain this design style, but also to stimulate you to contrib- ute to this progress. We believe the approach will work for explicitly parallel computers of the future just as it worked for the implicitly parallel computers of the past. In the 1960s, the dominant form of computing was on large mainframescom- puters costing millions of dollars and stored in computer rooms with multiple operators overseeing their support. Typical applications included business data processing and large-scale scientic computing. The 1970s saw the birth of the minicomputer, a smaller-sized computer initially focused on applications in scientic laboratories, but rapidly branching out with the popularity of time- sharingmultiple users sharing a computer interactively through independent terminals. That decade also saw the emergence of supercomputers, which were high-performance computers for scientic computing. Although few in number, they were important historically because they pioneered innovations that later trickled down to less expensive computer classes. The 1980s saw the rise of the desktop computer based on microprocessors, in the form of both personal computers and workstations. The individually owned desktop computer replaced time-sharing and led to the rise of serverscomputers that provided larger-scale services such as reliable, long-term le storage and access, larger memory, and more computing power. The 1990s saw the emergence of the Internet and the World Wide Web, the rst successful handheld computing devices (personal digi- 1.2 Classes of Computers 33. 1.2 Classes of Computers I 5 tal assistants or PDAs), and the emergence of high-performance digital consumer electronics, from video games to set-top boxes. The extraordinary popularity of cell phones has been obvious since 2000, with rapid improvements in functions and sales that far exceed those of the PC. These more recent applications use embedded computers, where computers are lodged in other devices and their presence is not immediately obvious. These changes have set the stage for a dramatic change in how we view computing, computing applications, and the computer markets in this new century. Not since the creation of the personal computer more than 20 years ago have we seen such dramatic changes in the way computers appear and in how they are used. These changes in computer use have led to three different computing markets, each characterized by different applications, requirements, and computing technologies. Figure 1.2 summarizes these mainstream classes of computing environments and their important characteristics. Desktop Computing The rst, and still the largest market in dollar terms, is desktop computing. Desk- top computing spans from low-end systems that sell for under $500 to high-end, heavily congured workstations that may sell for $5000. Throughout this range in price and capability, the desktop market tends to be driven to optimize price- performance. This combination of performance (measured primarily in terms of compute performance and graphics performance) and price of a system is what matters most to customers in this market, and hence to computer designers. As a result, the newest, highest-performance microprocessors and cost-reduced microprocessors often appear rst in desktop systems (see Section 1.6 for a discussion of the issues affecting the cost of computers). Desktop computing also tends to be reasonably well characterized in terms of applications and benchmarking, though the increasing use of Web-centric, interactive applications poses new challenges in performance evaluation. Feature Desktop Server Embedded Price of system $500$5000 $5000$5,000,000 $10$100,000 (including network routers at the high end) Price of microprocessor module $50$500 (per processor) $200$10,000 (per processor) $0.01$100 (per processor) Critical system design issues Price-performance, graphics performance Throughput, availability, scalability Price, power consumption, application-specic performance Figure 1.2 A summary of the three mainstream computing classes and their system characteristics. Note the wide range in system price for servers and embedded systems. For servers, this range arises from the need for very large-scale multiprocessor systems for high-end transaction processing and Web server applications.The total number of embedded processors sold in 2005 is estimated to exceed 3 billion if you include 8-bit and 16-bit microprocessors.Perhaps 200 million desktop computers and 10 million servers were sold in 2005. 34. 6 I Chapter One Fundamentals of Computer Design Servers As the shift to desktop computing occurred, the role of servers grew to provide larger-scale and more reliable le and computing services. The World Wide Web accelerated this trend because of the tremendous growth in the demand and sophistication of Web-based services. Such servers have become the backbone of large-scale enterprise computing, replacing the traditional mainframe. For servers, different characteristics are important. First, dependability is critical. (We discuss dependability in Section 1.7.) Consider the servers running Google, taking orders for Cisco, or running auctions on eBay. Failure of such server systems is far more catastrophic than failure of a single desktop, since these servers must operate seven days a week, 24 hours a day. Figure 1.3 esti- mates revenue costs of downtime as of 2000. To bring costs up-to-date, Ama- zon.com had $2.98 billion in sales in the fall quarter of 2005. As there were about 2200 hours in that quarter, the average revenue per hour was $1.35 million. Dur- ing a peak hour for Christmas shopping, the potential loss would be many times higher. Hence, the estimated costs of an unavailable system are high, yet Figure 1.3 and the Amazon numbers are purely lost revenue and do not account for lost employee productivity or the cost of unhappy customers. A second key feature of server systems is scalability. Server systems often grow in response to an increasing demand for the services they support or an increase in functional requirements. Thus, the ability to scale up the computing capacity, the memory, the storage, and the I/O bandwidth of a server is crucial. Lastly, servers are designed for efcient throughput. That is, the overall performance of the serverin terms of transactions per minute or Web pages served Application Cost of downtime per hour (thousands of $) Annual losses (millions of $) with downtime of 1% (87.6 hrs/yr) 0.5% (43.8 hrs/yr) 0.1% (8.8 hrs/yr) Brokerage operations $6450 $565 $283 $56.5 Credit card authorization $2600 $228 $114 $22.8 Package shipping services $150 $13 $6.6 $1.3 Home shopping channel $113 $9.9 $4.9 $1.0 Catalog sales center $90 $7.9 $3.9 $0.8 Airline reservation center $89 $7.9 $3.9 $0.8 Cellular service activation $41 $3.6 $1.8 $0.4 Online network fees $25 $2.2 $1.1 $0.2 ATM service fees $14 $1.2 $0.6 $0.1 Figure 1.3 The cost of an unavailable system is shown by analyzing the cost of downtime (in terms of immediately lost revenue), assuming three different levels of availability, and that downtime is distributed uniformly. These data are from Kembel [2000] and were collected and analyzed by Contingency Planning Research. 35. 1.2 Classes of Computers I 7 per secondis what is crucial. Responsiveness to an individual request remains important, but overall efciency and cost-effectiveness, as determined by how many requests can be handled in a unit time, are the key metrics for most servers. We return to the issue of assessing performance for different types of computing environments in Section 1.8. A related category is supercomputers. They are the most expensive computers, costing tens of millions of dollars, and they emphasize oating-point performance. Clusters of desktop computers, which are discussed in Appendix H, have largely overtaken this class of computer. As clusters grow in popularity, the number of conventional supercomputers is shrinking, as are the number of companies who make them. Embedded Computers Embedded computers are the fastest growing portion of the computer market. These devices range from everyday machinesmost microwaves, most washing machines, most printers, most networking switches, and all cars contain simple embedded microprocessorsto handheld digital devices, such as cell phones and smart cards, to video games and digital set-top boxes. Embedded computers have the widest spread of processing power and cost. They include 8-bit and 16-bit processors that may cost less than a dime, 32-bit microprocessors that execute 100 million instructions per second and cost under $5, and high-end processors for the newest video games or network switches that cost $100 and can execute a billion instructions per second. Although the range of computing power in the embedded computing market is very large, price is a key factor in the design of computers for this space. Performance requirements do exist, of course, but the primary goal is often meeting the performance need at a minimum price, rather than achieving higher performance at a higher price. Often, the performance requirement in an embedded application is real-time execution. A real-time performance requirement is when a segment of the application has an absolute maximum execution time. For example, in a digital set-top box, the time to process each video frame is limited, since the processor must accept and process the next frame shortly. In some applications, a more nuanced requirement exists: the average time for a particular task is constrained as well as the number of instances when some maximum time is exceeded. Such approachessometimes called soft real-timearise when it is possible to occa- sionally miss the time constraint on an event, as long as not too many are missed. Real-time performance tends to be highly application dependent. Two other key characteristics exist in many embedded applications: the need to minimize memory and the need to minimize power. In many embedded applications, the memory can be a substantial portion of the system cost, and it is important to optimize memory size in such cases. Sometimes the application is expected to t totally in the memory on the processor chip; other times the 36. 8 I Chapter One Fundamentals of Computer Design application needs to t totally in a small off-chip memory. In any event, the importance of memory size translates to an emphasis on code size, since data size is dictated by the application. Larger memories also mean more power, and optimizing power is often critical in embedded applications. Although the emphasis on low power is frequently driven by the use of batteries, the need to use less expensive packagingplastic versus ceramicand the absence of a fan for cooling also limit total power consumption. We examine the issue of power in more detail in Section 1.5. Most of this book applies to the design, use, and performance of embedded processors, whether they are off-the-shelf microprocessors or microprocessor cores, which will be assembled with other special-purpose hardware. Indeed, the third edition of this book included examples from embedded computing to illustrate the ideas in every chapter. Alas, most readers found these examples unsatisfactory, as the data that drives the quantitative design and evaluation of desktop and server computers has not yet been extended well to embedded computing (see the challenges with EEMBC, for example, in Section 1.8). Hence, we are left for now with qualitative descriptions, which do not t well with the rest of the book. As a result, in this edition we consolidated the embedded material into a single appendix. We believe this new appendix (Appendix D) improves the ow of ideas in the text while still allowing readers to see how the differing requirements affect embedded computing. The task the computer designer faces is a complex one: Determine what attributes are important for a new computer, then design a computer to maximize performance while staying within cost, power, and availability constraints. This task has many aspects, including instruction set design, functional organization, logic design, and implementation. The implementation may encompass integrated circuit design, packaging, power, and cooling. Optimizing the design requires familiarity with a very wide range of technologies, from compilers and operating systems to logic design and packaging. In the past, the term computer architecture often referred only to instruction set design. Other aspects of computer design were called implementation, often insinuating that implementation is uninteresting or less challenging. We believe this view is incorrect. The architects or designers job is much more than instruction set design, and the technical hurdles in the other aspects of the project are likely more challenging than those encountered in instruction set design. Well quickly review instruction set architecture before describing the larger challenges for the computer architect. Instruction Set Architecture We use the term instruction set architecture (ISA) to refer to the actual programmer- visible instruction set in this book. The ISA serves as the boundary between the 1.3 Dening Computer Architecture 37. 1.3 Dening Computer Architecture I 9 software and hardware. This quick review of ISA will use examples from MIPS and 80x86 to illustrate the seven dimensions of an ISA. Appendices B and J give more details on MIPS and the 80x86 ISAs. 1. Class of ISANearly all ISAs today are classied as general-purpose register architectures, where the operands are either registers or memory locations. The 80x86 has 16 general-purpose registers and 16 that can hold oating- point data, while MIPS has 32 general-purpose and 32 oating-point registers (see Figure 1.4). The two popular versions of this class are register-memory ISAs such as the 80x86, which can access memory as part of many instructions, and load-store ISAs such as MIPS, which can access memory only with load or store instructions. All recent ISAs are load-store. 2. Memory addressingVirtually all desktop and server computers, including the 80x86 and MIPS, use byte addressing to access memory operands. Some architectures, like MIPS, require that objects must be aligned. An access to an object of size s bytes at byte address A is aligned if A mod s = 0. (See Figure B.5 on page B-9.) The 80x86 does not require alignment, but accesses are generally faster if operands are aligned. 3. Addressing modesIn addition to specifying registers and constant operands, addressing modes specify the address of a memory object. MIPS addressing modes are Register, Immediate (for constants), and Displacement, where a constant offset is added to a register to form the memory address. The 80x86 supports those three plus three variations of displacement: no register (absolute), two registers (based indexed with displacement), two registers where Name Number Use Preserved across a call? $zero 0 The constant value 0 N.A. $at 1 Assembler temporary No $v0$v1 23 Values for function results and expression evaluation No $a0$a3 47 Arguments No $t0$t7 815 Temporaries No $s0$s7 1623 Saved temporaries Yes $t8$t9 2425 Temporaries No $k0$k1 2627 Reserved for OS kernel No $gp 28 Global pointer Yes $sp 29 Stack pointer Yes $fp 30 Frame pointer Yes $ra 31 Return address Yes Figure 1.4 MIPS registers and usage conventions. In addition to the 32 general- purpose registers (R0R31), MIPS has 32 oating-point registers (F0F31) that can hold either a 32-bit single-precision number or a 64-bit double-precision number. 38. 10 I Chapter One Fundamentals of Computer Design one register is multiplied by the size of the operand in bytes (based with scaled index and displacement). It has more like the last three, minus the displacement eld: register indirect, indexed, and based with scaled index. 4. Types and sizes of operandsLike most ISAs, MIPS and 80x86 support operand sizes of 8-bit (ASCII character), 16-bit (Unicode character or half word), 32-bit (integer or word), 64-bit (double word or long integer), and IEEE 754 oating point in 32-bit (single precision) and 64-bit (double precision). The 80x86 also supports 80-bit oating point (extended double precision). 5. OperationsThe general categories of operations are data transfer, arithmetic logical, control (discussed next), and oating point. MIPS is a simple and easy-to-pipeline instruction set architecture, and it is representative of the RISC architectures being used in 2006. Figure 1.5 summarizes the MIPS ISA. The 80x86 has a much richer and larger set of operations (see Appendix J). 6. Control ow instructionsVirtually all ISAs, including 80x86 and MIPS, support conditional branches, unconditional jumps, procedure calls, and returns. Both use PC-relative addressing, where the branch address is speci- ed by an address eld that is added to the PC. There are some small differences. MIPS conditional branches (BE, BNE, etc.) test the contents of registers, while the 80x86 branches (JE, JNE, etc.) test condition code bits set as side effects of arithmetic/logic operations. MIPS procedure call (JAL) places the return address in a register, while the 80x86 call (CALLF) places the return address on a stack in memory. 7. Encoding an ISAThere are two basic choices on encoding: xed length and variable length. All MIPS instructions are 32 bits long, which simplies instruction decoding. Figure 1.6 shows the MIPS instruction formats. The 80x86 encoding is variable length, ranging from 1 to 18 bytes. Variable- length instructions can take less space than xed-length instructions, so a program compiled for the 80x86 is usually smaller than the same program compiled for MIPS. Note that choices mentioned above will affect how the instructions are encoded into a binary representation. For example, the number of registers and the number of addressing modes both have a signicant impact on the size of instructions, as the register eld and addressing mode eld can appear many times in a single instruction. The other challenges facing the computer architect beyond ISA design are particularly acute at the present, when the differences among instruction sets are small and when there are distinct application areas. Therefore, starting with this edition, the bulk of instruction set material beyond this quick review is found in the appendices (see Appendices B and J). We use a subset of MIPS64 as the example ISA in this book. 39. 1.3 Dening Computer Architecture I 11 Instruction type/opcode Instruction meaning Data transfers Move data between registers and memory, or between the integer and FP or special registers; only memory address mode is 16-bit displacement + contents of a GPR LB, LBU, SB Load byte, load byte unsigned, store byte (to/from integer registers) LH, LHU, SH Load half word, load half word unsigned, store half word (to/from integer registers) LW, LWU, SW Load word, load word unsigned, store word (to/from integer registers) LD, SD Load double word, store double word (to/from integer registers) L.S, L.D, S.S, S.D Load SP oat, load DP oat, store SP oat, store DP oat MFC0, MTC0 Copy from/to GPR to/from a special register MOV.S, MOV.D Copy one SP or DP FP register to another FP register MFC1, MTC1 Copy 32 bits to/from FP registers from/to integer registers Arithmetic/logical Operations on integer or logical data in GPRs; signed arithmetic trap on overow DADD, DADDI, DADDU, DADDIU Add, add immediate (all immediates are 16 bits); signed and unsigned DSUB, DSUBU Subtract; signed and unsigned DMUL, DMULU, DDIV, DDIVU, MADD Multiply and divide, signed and unsigned; multiply-add; all operations take and yield 64-bit values AND, ANDI And, and immediate OR, ORI, XOR, XORI Or, or immediate, exclusive or, exclusive or immediate LUI Load upper immediate; loads bits 32 to 47 of register with immediate, then sign-extends DSLL, DSRL, DSRA, DSLLV, DSRLV, DSRAV Shifts: both immediate (DS__) and variable form (DS__V); shifts are shift left logical, right logical, right arithmetic SLT, SLTI, SLTU, SLTIU Set less than, set less than immediate; signed and unsigned Control Conditional branches and jumps; PC-relative or through register BEQZ, BNEZ Branch GPRs equal/not equal to zero; 16-bit offset from PC + 4 BEQ, BNE Branch GPR equal/not equal; 16-bit offset from PC + 4 BC1T, BC1F Test comparison bit in the FP status register and branch; 16-bit offset from PC + 4 MOVN, MOVZ Copy GPR to another GPR if third GPR is negative, zero J, JR Jumps: 26-bit offset from PC + 4 (J) or target in register (JR) JAL, JALR Jump and link: save PC + 4 in R31, target is PC-relative (JAL) or a register (JALR) TRAP Transfer to operating system at a vectored address ERET Return to user code from an exception; restore user mode Floating point FP operations on DP and SP formats ADD.D, ADD.S, ADD.PS Add DP, SP numbers, and pairs of SP numbers SUB.D, SUB.S, SUB.PS Subtract DP, SP numbers, and pairs of SP numbers MUL.D, MUL.S, MUL.PS Multiply DP, SP oating point, and pairs of SP numbers MADD.D, MADD.S, MADD.PS Multiply-add DP, SP numbers, and pairs of SP numbers DIV.D, DIV.S, DIV.PS Divide DP, SP oating point, and pairs of SP numbers CVT._._ Convert instructions: CVT.x.y converts from type x to type y, where x and y are L (64-bit integer), W (32-bit integer), D (DP), or S (SP). Both operands are FPRs. C.__.D, C.__.S DP and SP compares: __ = LT,GT,LE,GE,EQ,NE; sets bit in FP status register Figure 1.5 Subset of the instructions in MIPS64. SP = single precision; DP = double precision. Appendix B gives much more detail on MIPS64.For data,the most signicant bit number is 0; least is 63. 40. 12 I Chapter One Fundamentals of Computer Design The Rest of Computer Architecture: Designing the Organization and Hardware to Meet Goals and Functional Requirements The implementation of a computer has two components: organization and hardware. The term organization includes the high-level aspects of a computers design, such as the memory system, the memory interconnect, and the design of the internal processor or CPU (central processing unitwhere arithmetic, logic, branching, and data transfer are implemented). For example, two processors with the same instruction set architectures but very different organizations are the AMD Opteron 64 and the Intel Pentium 4. Both processors implement the x86 instruction set, but they have very different pipeline and cache organizations. Hardware refers to the specics of a computer, including the detailed logic design and the packaging technology of the computer. Often a line of computers contains computers with identical instruction set architectures and nearly identical organizations, but they differ in the detailed hardware implementation. For example, the Pentium 4 and the Mobile Pentium 4 are nearly identical, but offer different clock rates and different memory systems, making the Mobile Pentium 4 more effective for low-end computers. In this book, the word architecture covers all three aspects of computer designinstruction set architecture, organization, and hardware. Computer architects must design a computer to meet functional requirements as well as price, power, performance, and availability goals. Figure 1.7 summarizes requirements to consider in designing a new computer. Often, architects Figure 1.6 MIPS64 instruction set architecture formats. All instructions are 32 bits long.The R format is for integer register-to-register operations,such as DADDU,DSUBU, and so on.The I format is for data transfers, branches, and immediate instructions, such as LD, SD, BEQZ, and DADDIs.The J format is for jumps, the FR format for oating point operations,and the FI format for oating point branches. Basic instruction formats R opcode rs rt rd shamt funct 31 026 25 21 20 16 15 11 10 6 5 I opcode rs rt immediate 31 26 25 21 20 16 15 J opcode address 31 26 25 Floating-point instruction formats FR opcode fmt ft fs fd funct 31 026 25 21 20 16 15 11 10 6 5 FI opcode fmt ft immediate 31 26 25 21 20 16 15 41. 1.3 Dening Computer Architecture I 13 also must determine what the functional requirements are, which can be a major task. The requirements may be specic features inspired by the market. Applica- tion software often drives the choice of certain functional requirements by determining how the computer will be used. If a large body of software exists for a certain instruction set architecture, the architect may decide that a new computer should implement an existing instruction set. The presence of a large market for a particular class of applications might encourage the designers to incorporate requirements that would make the computer competitive in that market. Many of these requirements and features are examined in depth in later chapters. Architects must also be aware of important trends in both the technology and the use of computers, as such trends not only affect future cost, but also the lon- gevity of an architecture. Functional requirements Typical features required or supported Application area Target of computer General-purpose desktop Balanced performance for a range of tasks, including interactive performance for graphics, video, and audio (Ch. 2, 3, 5, App. B) Scientic desktops and servers High-performance oating point and graphics (App. I) Commercial servers Support for databases and transaction processing; enhancements for reliability and availability; support for scalability (Ch. 4, App. B, E) Embedded computing Often requires special support for graphics or video (or other application-specic extension); power limitations and power control may be required (Ch. 2, 3, 5,App. B) Level of software compatibility Determines amount of existing software for computer At programming language Most exible for designer; need new compiler (Ch. 4, App. B) Object code or binary compatible Instruction set architecture is completely denedlittle exibilitybut no investment needed in software or porting programs Operating system requirements Necessary features to support chosen OS (Ch. 5, App. E) Size of address space Very important feature (Ch. 5); may limit applications Memory management Required for modern OS; may be paged or segmented (Ch. 5) Protection Different OS and application needs: page vs. segment; virtual machines (Ch. 5) Standards Certain standards may be required by marketplace Floating point Format and arithmetic: IEEE 754 standard (App. I), special arithmetic for graphics or signal processing I/O interfaces For I/O devices: Serial ATA, Serial Attach SCSI, PCI Express (Ch. 6, App. E) Operating systems UNIX, Windows, Linux, CISCO IOS Networks Support required for different networks: Ethernet, Inniband (App. E) Programming languages Languages (ANSI C, C++, Java, FORTRAN) affect instruction set (App. B) Figure 1.7 Summary of some of the most important functional requirements an architect faces.The left-hand column describes the class of requirement, while the right-hand column gives specic examples.The right-hand column also contains references to chapters and appendices that deal with the specic issues. 42. 14 I Chapter One Fundamentals of Computer Design If an instruction set architecture is to be successful, it must be designed to survive rapid changes in computer technology. After all, a successful new instruction set architecture may last decadesfor example, the core of the IBM mainframe has been in use for more than 40 years. An architect must plan for technology changes that can increase the lifetime of a successful computer. To plan for the evolution of a computer, the designer must be aware of rapid changes in implementation technology. Four implementation technologies, which change at a dramatic pace, are critical to modern implementations: I Integrated circuit logic technologyTransistor density increases by about 35% per year, quadrupling in somewhat over four years. Increases in die size are less predictable and slower, ranging from 10% to 20% per year. The combined effe