[PDF Download] Computer organization and architecture 9th edition william stallings full chapter pdf
Computer Organization and Architecture 9th Edition William Stallings
Visit to download the full and correct content document: https://textbookfull.com/product/computer-organization-and-architecture-9th-edition-wi lliam-stallings/
More products digital (pdf, epub, mobi) instant download maybe you interests ...
Computer Organization and Architecture Designing for Performance 10th Edition William Stallings
Modern Computer Architecture and Organization Learn x86 ARM and RISC V architectures and the design of smartphones PCs and cloud servers 2nd Edition Ledin
Many of the designations by manufacturers and sellers to distinguish their products are claimed as trademarks. Where those designations appear in this book, and the publisher was aware of a trademark claim, the designations have been printed in initial caps or all caps.
ISBN 10: 0-13-293633-X
ISBN 13: 978-0-13-293633-0
To Tricia (ATS), my loving wife, the kindest and gentlest person
This page intentionally left blank
CONTENTS
Online Resources xi
Preface xiii
About the Author xxi
Chapter 0 Reader’s and Instructor’s Guide 1
0.1 Outline of the Book 2
0.2 A Roadmap for Readers and Instructors 2
0.3 Why Study Computer Organization and Architecture? 3
0.4 Internet and Web Resources 5
PART ONE OVERVIEW 6
Chapter 1 Introduction 6
1.1 Organization and Architecture 7
1.2 Structure and Function 8
1.3 Key Terms and Review Questions 14
Chapter 2 Computer Evolution and Performance 15
2.1 A Brief History of Computers 16
2.2 Designing for Performance 37
2.3 Multicore, MICs, and GPGPUs 43
2.4 The Evolution of the Intel x86 Architecture 44
2.5 Embedded Systems and the ARM 45
2.6 Performance Assessment 49
2.7 Recommended Reading 59
2.8 Key Terms, Review Questions, and Problems 60
PART TWO THE COMPUTER SYSTEM 65
Chapter 3 A Top-Level View of Computer Function and Interconnection 65
3.1 Computer Components 66
3.2 Computer Function 68
3.3 Interconnection Structures 84
3.4 Bus Interconnection 85
3.5 Point-To-Point Interconnect 93
3.6 PCI Express 98
3.7 Recommended Reading 108
3.8 Key Terms, Review Questions, and Problems 108
Chapter 4 Cache Memory 112
4.1 Computer Memory System Overview 113
4.2 Cache Memory Principles 120
4.3 Elements of Cache Design 123
4.4 Pentium 4 Cache Organization 141
4.5 ARM Cache Organization 144
4.6 Recommended Reading 146
4.7 Key Terms, Review Questions, and Problems 147
Chapter 5
Appendix 4A Performance Characteristics of Two-Level Memories 152
Internal Memory 159
5.1 Semiconductor Main Memory 160
5.2 Error Correction 170
5.3 Advanced DRAM Organization 174
5.4 Recommended Reading 180
5.5 Key Terms, Review Questions, and Problems 181
Chapter 6 External Memory 185
6.1 Magnetic Disk 186
6.2 RAID 195
6.3 Solid State Drives 205
6.4 Optical Memory 210
6.5 Magnetic Tape 215
6.6 Recommended Reading 217
6.7 Key Terms, Review Questions, and Problems 218
Chapter 7 Input/Output 221
7.1 External Devices 223
7.2 I/O Modules 226
7.3 Programmed I/O 228
7.4 Interrupt-Driven I/O 232
7.5 Direct Memory Access 240
7.6 I/O Channels and Processors 246
7.7 The External Interface: Thunderbolt and Infiniband 248
7.8 IBM zEnterprise 196 I/O Structure 256
7.9 Recommended Reading 260
7.10 Key Terms, Review Questions, and Problems 260
Chapter 8 Operating System Support 265
8.1 Operating System Overview 266
8.2 Scheduling 277
8.3 Memory Management 283
8.4 Pentium Memory Management 294
8.5 ARM Memory Management 299
8.6 Recommended Reading 304
8.7 Key Terms, Review Questions, and Problems 304
PART THREE ARITHMETIC AND LOGIC 309
Chapter 9 Number Systems 309
9.1 The Decimal System 310
9.2 Positional Number Systems 311
9.3 The Binary System 312
9.4 Converting Between Binary and Decimal 312
9.5 Hexadecimal Notation 315
9.6 Recommended Reading 317
9.7 Key Terms and Problems 317
Chapter 10 Computer Arithmetic 319
10.1 The Arithmetic and Logic Unit 320
10.2 Integer Representation 321
10.3 Integer Arithmetic 326
10.4 Floating-Point Representation 341
10.5 Floating-Point Arithmetic 349
10.6 Recommended Reading 358
10.7 Key Terms, Review Questions, and Problems 359
Chapter 11 Digital Logic 364
11.1 Boolean Algebra 365
11.2 Gates 368
11.3 Combinational Circuits 370
11.4 Sequential Circuits 388
11.5 Programmable Logic Devices 397
11.6 Recommended Reading 401
11.7 Key Terms and Problems 401
PART FOUR THE CENTRAL PROCESSING UNIT 405
Chapter 12 Instruction Sets: Characteristics and Functions 405
12.1 Machine Instruction Characteristics 406
12.2 Types of Operands 413
12.3 Intel x86 and ARM Data Types 415
12.4 Types of Operations 418
12.5 Intel x86 and ARM Operation Types 431
12.6 Recommended Reading 441
12.7 Key Terms, Review Questions, and Problems 441 Appendix 12A Little-, Big-, and Bi-Endian 447
Chapter 13 Instruction Sets: Addressing Modes and Formats 451
13.1 Addressing Modes 452
13.2 x86 and ARM Addressing Modes 459
13.3 Instruction Formats 464
13.4 x86 and ARM Instruction Formats 473
13.5 Assembly Language 477
13.6 Recommended Reading 479
13.7 Key Terms, Review Questions, and Problems 479
Chapter 14 Processor Structure and Function 483
14.1 Processor Organization 484
14.2 Register Organization 486
14.3 Instruction Cycle 491
14.4 Instruction Pipelining 495
14.5 The x86 Processor Family 512
14.6 The ARM Processor 520
14.7 Recommended Reading 526
14.8 Key Terms, Review Questions, and Problems 527
Chapter 15 Reduced Instruction Set Computers 531
15.1 Instruction Execution Characteristics 533
15.2 The Use of a Large Register File 538
15.3 Compiler-Based Register Optimization 543
15.4 Reduced Instruction Set Architecture 545
15.5 RISC Pipelining 551
15.6 MIPS R4000 556
15.7 SPARC 562
15.8 RISC Versus CISC Controversy 568
15.9 Recommended Reading 569
15.10 Key Terms, Review Questions, and Problems 569
Chapter 16 Instruction-Level Parallelism and Superscalar Processors 573
16.1 Overview 574
16.2 Design Issues 579
16.3 Pentium 4 589
16.4 ARM Cortex-A8 595
16.5 Recommended Reading 603
16.6 Key Terms, Review Questions, and Problems 605
PART FIVE PARALLEL ORGANIZATION 611
Chapter 17 Parallel Processing 611
17.1 Multiple Processor Organizations 613
17.2 Symmetric Multiprocessors 615
17.3 Cache Coherence and the MESI Protocol 619
17.4 Multithreading and Chip Multiprocessors 626
17.5 Clusters 633
17.6 Nonuniform Memory Access 640
17.7 Vector Computation 644
17.8 Recommended Reading 656
17.9 Key Terms, Review Questions, and Problems 657
Chapter 18 Multicore Computers 664
18.1 Hardware Performance Issues 665
18.2 Software Performance Issues 669
18.3 Multicore Organization 674
18.4 Intel x86 Multicore Organization 676
18.5 ARM11 MPCore 679
18.6 IBM zEnterprise 196 Mainframe 684
18.7 Recommended Reading 687
18.8 Key Terms, Review Questions, and Problems 687
Appendix A Projects for Teaching Computer Organization and Architecture 691
A.1 Interactive Simulations 692
A.2 Research Projects 694
A.3 Simulation Projects 694
A.4 Assembly Language Projects 695
A.5 Reading/Report Assignments 696
A.6 Writing Assignments 696
A.7 Test Bank 696
Appendix B Assembly Language and Related Topics 697
B.1 Assembly Language 698
B.2 Assemblers 706
B.3 Loading and Linking 710
B.4 Recommended Reading 718
B.5 Key Terms, Review Questions, and Problems 719
ONLINE CHAPTERS1
PART SIX THE CONTROL UNIT 19-1
Chapter 19 Control Unit Operation 19-1
19.1 Micro-operations 19-3
19.2 Control of the Processor 19-13
19.3 Hardwired Implementation 19-30
19.4 Recommended Reading 19-35
19.5 Key Terms, Review Questions, and Problems 19-35
Chapter 20 Microprogrammed Control 20-1
20.1 Basic Concepts 20-3
20.2 Microinstruction Sequencing 20-16
20.3 Microinstruction Execution 20-26
20.4 TI 8800 20-45
20.5 Recommended Reading 20-59
20.6 Key Terms, Review Questions, and Problems 20-60
Appendix C Hash Tables
ONLINE APPENDICES
Appendix D Victim Cache Strategies
D.1 Victim Cache
D.2 Selective Victim Cache
1Online chapters, appendices, and other documents are Premium Content, available via the access card at the front of this book.
Appendix E Interleaved Memory
Appendix F The International Reference Alphabet
Appendix G Virtual Memory Page Replacement Algorithms
G.1 Optimal
G.2 Least Recently Used
G.3 First-In-First-Out
G.4 Other Page Replacement Algorithms
Appendix H Recursive Procedures
H.1 Recursion
H.2 Activation Tree Representation
H.3 Stack Processing
H.4 Recursion and Iteration
Appendix I Additional Instruction Pipeline Topics
I.1 Pipeline Reservation Tables
I.2 Reorder Buffers
I.3 Tomasulo’s Algorithm
I.4 Scoreboarding
Appendix J Linear Tape Open Technology
J.1 LTO Generations
J.2 LTO Format
J.3 LTO Operation
Appendix K DDR SRAM
Appendix L Protocols and Protocol Architectures
L.1 Introduction
L.2 The TCP/IP Protocol Architecture
L.3 The Role of an Internet Protocol
L.4 IPv4
L.5 IPv6
L.6 The OSI Protocol Architecture
Appendix M Scrambling
Appendix N Timing Diagrams
Appendix O Stacks
O.1 Stack Structure
O.2 Stack Implementation
O.3 Expression Evaluation
Glossary 723
References 733
Index 745
ONLINE RESOURCES
Site Location
Companion Website
Premium Content
Instructor Resource Center (IRC)
Computer Science Student Resource Site
WilliamStallings.com/ ComputerOrganization
Click on Premium Content link at Companion Website or at pearsonhighered.com/stallings and enter the student access code found on the card in the front of the book.
Click on Pearson Resources for Instructors link at Companion Website or on Instructor Resource link at pearsonhighered.com/stallings.
Description
Student Resources link: Useful links and documents for students.
Instructor Resources link: Useful links and documents for instructors.
Online chapters, appendices, and other documents that supplement the book.
Solutions manual, projects manual, slides, and other useful documents.
ComputerScienceStudent.comUseful links and documents for computer science students.
This page intentionally left blank
PREFACE
WHAT’S NEW IN THE NINTH EDITION
In the four years since the eighth 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 eighth edition of this book was extensively reviewed by a number of professors who teach the subject and by professionals working in the field. The result is that, in many places, the narrative has been clarified and tightened, and illustrations have been improved.
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. The most noteworthy changes are as follows:
• Point-to-point interconnect: The traditional bus architecture has increasingly been replaced with high-speed point-to-point interconnect schemes. A new section explores this technology, using Intel’s QuickPath Interconnect (QPI) as an example.
• PCI Express: PCI Express (PCIe) has become a standard peripheral interconnect architecture, replacing PCI and other bus-based architectures. A new section covers PCIe.
• Solid state drive and flash memory: Solid state drives are increasingly displacing hard disk drives over a range of computers. A new section covers SSDs and the underlying flash memory technology.
• IEEE 754 Floating-Point Standard: The coverage of IEEE 754 has been updated to reflect the 2008 standard.
• Contemporary mainframe organization: Chapters 7 and 18 include sections on the zEnterprise 196, IBM’s latest mainframe computer offering (at the time of this writing), introduced in 2010.
• I/O standards: The book has been updated to reflect the latest developments, including Thunderbolt.
• Multicore architecture: The material on multicore architecture has been expanded significantly.
• Student study aids: Each chapter now begins with a list of learning objectives.
• Sample syllabus: The text contains more material than can be conveniently covered in one semester. Accordingly, instructors are provided with several sample syllabi that guide the use of the text within limited time (e.g., 16 weeks or 12 weeks). These samples are based on real-world experience by professors with the eighth edition.
• Test bank: A set of review questions, including yes/no, multiple choice, and fill in the blank is provided for each chapter.
With each new edition it is a struggle to maintain a reasonable page count while adding new material. In part this objective is realized by eliminating obsolete material and tightening the narrative. For this edition, chapters and appendices that are of less general interest have been moved online, as individual PDF files. This has allowed an expansion of material without the corresponding increase in size and price.
OBJECTIVES
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 also 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. All 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, I/O.
• Processor: Major components are control unit, registers, ALU, and instruction execution unit.
• Control unit: Provides control signals for the operation and coordination of all processor components. Traditionally, a microprogramming implementation has been used, in which major components are control memory, microinstruction sequencing logic, and registers. More recently, microprogramming has been less prominent but remains an important implementation technique.
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 text is intended to acquaint the reader with the design principles and implementation issues of contemporary operating systems. Accordingly, a purely conceptual or theoretical treatment would be inadequate. To illustrate the concepts and to tie them to real-world design choices that must be made, two processor families have been chosen as running examples:
• Intel x86 architecture: The x86 architecture is the most widely used for nonembedded computer systems. The x86 is essentially a complex instruction set computer (CISC) with some RISC features. Recent members of the x86 family make use of superscalar and multicore design principles. The evolution of features in the x86 architecture provides a unique case study of the evolution of most of the design principles in computer architecture.
• ARM: The ARM architecture is arguably the most widely used embedded processor, used in cell phones, iPods, remote sensor equipment, and many other devices. The ARM is essentially a reduced instruction set computer (RISC). Recent members of the ARM family make use of superscalar and multicore design principles. Many, but by no means all, of the examples in this book are drawn from these two computer families. Numerous other systems, both contemporary and historical, provide examples of important computer architecture design features.
PLAN OF THE TEXT
The book is organized into six parts (see Chapter 0 for an overview):
• Overview
• The computer system
• Arithmetic and logic
• The central processing unit
• Parallel organization, including multicore
• The control unit
The book includes a number of pedagogic features, including the use of interactive simulations and numerous figures and tables to clarify the discussion. Each chapter includes a list of key words, review questions, homework problems, and suggestions for further reading. The book also includes an extensive glossary, a list of frequently used acronyms, and a bibliography.
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 core topics in the body of knowledge category, Architecture and Organization, in the IEEE/ACM Computer Curriculum 2008: An Interim Revision to CS 2001 . This book also covers the core area CE-CAO Computer Architecture and Organization from the IEEE/ACM Computer Engineering Curriculum Guidelines 2004.
For the professional interested in this field, the book serves as a basic reference volume and is suitable for self-study.
INSTRUCTOR SUPPORT MATERIALS
Support materials for instructors are available at the Instructor Resource Center (IRC) for this textbook, which can be reached through the Publisher’s Website www.pearsonhighered .com/stallings or by clicking on the link labeled “Pearson Resources for Instructors” at this book’s Companion Website at WilliamStallings.com/ComputerOrganization. To gain access to the IRC, please contact your local Pearson sales representative via pearsonhighered .com/educator/replocator/requestSalesRep.page or call Pearson Faculty Services at 1-800-526-0485. The IRC provides the following materials:
• Projects manual: Project resources including documents and portable software, plus suggested project assignments for all of the project categories listed subsequently in this Preface.
• Solutions manual: Solutions to end-of-chapter Review Questions and Problems.
• PowerPoint slides: A set of slides covering all chapters, suitable for use in lecturing.
• PDF files: Copies of all figures and tables from the book.
• Test bank: A chapter-by-chapter set of questions.
• Sample syllabuses: The text contains more material than can be conveniently covered in one semester. Accordingly, instructors are provided with several sample syllabuses that guide the use of the text within limited time. These samples are based on realworld experience by professors with the first edition.
The Companion Website , at WilliamStallings.com/ComputerOrganization (click on Instructor Resources link) includes the following:
• Links to Websites for other courses being taught using this book.
• Sign-up information for an Internet mailing list for instructors using this book to exchange information, suggestions, and questions with each other and with the author.
STUDENT RESOURCES
For this new edition, a tremendous amount of original supporting material for students has been made available online, at two Web locations. The Companion Website , at WilliamStallings.com/ComputerOrganization (click on Student Resources link), includes a list of relevant links organized by chapter and an errata sheet for the book. Purchasing this textbook new grants the reader six months of access to the Premium Content Site, which includes the following materials:
• Online chapters: To limit the size and cost of the book, two chapters of the book are provided in PDF format. The chapters are listed in this book’s table of contents.
• Online appendices: There are numerous interesting topics that support material found in the text but whose inclusion is not warranted in the printed text. A total of 13 appendices cover these topics for the interested student. The appendices are listed in this book’s table of contents.
• Homework problems and solutions: To aid the student in understanding the material, a separate set of homework problems with solutions are available. Students can enhance their understanding of the material by working out the solutions to these problems and then checking their answers.
• Key papers: Several dozen papers from the professional literature, many hard to find, are provided for further reading.
• Supporting documents: A variety of other useful documents are referenced in the text and provided online.
Finally, I maintain the Computer Science Student Resource Site at WilliamStallings .com/StudentSupport.html.
PROJECTS AND OTHER STUDENT EXERCISES
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 support materials available through Prentice Hall not only includes guidance on how to assign and structure the projects but also includes a set of user’s manuals for various project types plus specific assignments, all written especially for this book. Instructors can assign work in the following areas:
• Interactive simulation assignments: Described subsequently.
• Research projects: A series of research assignments that instruct the student to research a particular topic on the Internet and write a report.
• Simulation projects: The IRC 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.
• Assembly language projects: A simplified assembly language, CodeBlue, is used and assignments based on the popular Core Wars concept are provided.
• Reading/report assignments: 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.
• Writing assignments: A list of writing assignments to facilitate learning the material.
• Test bank: Includes T/F, multiple choice, and fill-in-the-blanks questions and answers.
This diverse set of projects and other student exercises enables the instructor to use the book as one component in a rich and varied learning experience and to tailor a course plan to meet the specific needs of the instructor and students. See Appendix A in this book for details.
INTERACTIVE SIMULATIONS
An important feature in this edition is the incorporation of interactive simulations. These simulations provide a powerful tool for understanding the complex design features of a modern computer system. A total of 20 interactive simulations are used to illustrate key functions and algorithms in computer organization and architecture design. At the relevant point in the book, an icon indicates that a relevant interactive simulation is available online for student use. Because the animations enable the user to set initial conditions, they can serve as the basis for student assignments. The instructor’s supplement includes a set of assignments, one for each of the animations. Each assignment includes several specific problems that can be assigned to students. For access to the animations, click on the rotating globe at this book’s Website at http://williamstallings.com/ComputerOrganization.
ACKNOWLEDGMENTS
This new edition has benefited from review by a number of people, who gave generously of their time and expertise. The following professors and instructors reviewed all or a large part of the manuscript: Branson Murrill (Virginia Commonwealth University), Pan Deng (Florida International University), Bob Broeg (Western Oregon University), Curtis Meadow (University of Maine, Orono), Charles Weems (University of Massachusetts), and Mike Jochen (East Stroudsberg University).
Thanks also to the many people who provided detailed technical reviews of one or more chapters: Kauser Johar, Todd Bezenek (Quantum), Moustafa Mohamed (University of Colorado at Boulder), Dharmesh Parikh, Qigang Wang, Rajiv Dasmohapatra (WIPRO Ltd), Anup Holey (University of Minnesota, Twin Cities), Alexandre Keunecke Ignacio de Mendonca, Douglas Tiedt, Kursad Albayraktaroglu (Advanced Micro Device), Nilanjan Goswami (University of Florida, Gainesville), Adnan Khaleel (Cray, Inc.), Geri Lamble,
Liu Han, Mafijul Islam (Volvo Technology, Sweden), Roger Kahn, Brian Case, Mani Srinivasan, Abhishek Deb, Sushil Menon (University of Pennsylvania), Jigar Savla (Georgia Institute of Technology), Madhu Mutyam, Karl Stevens, Vineet Chadha (Intel Labs), Xingxing Jin (University of Saskatchewan), Jan Hoogerbrugge (NXP Semiconductors), Ninad Laxman Sawant, Aziz Eker (TOBB University of Economics and Technology, Ankara, Turkey), Bhupati Shukla, Niket Choudhary (North Carolina State University), and Oguz Ergin (TOBB University of Economics and Technology, Ankara, Turkey).
Professor Cindy Norris of Appalachian State University, Professor Bin Mu of the University of New Brunswick, and Professor Kenrick Mock of the University of Alaska kindly supplied homework problems.
Aswin Sreedhar of the University of Massachusetts developed the interactive simulation assignments and also wrote the test bank.
Professor Miguel Angel Vega Rodriguez, Professor Dr. Juan Manuel Sánchez Pérez, and Professor Dr. Juan Antonio Gómez Pulido, all of University of Extremadura, Spain, prepared the SMPCache problems in the instructor’s manual and authored the SMPCache User’s Guide.
Todd Bezenek of the University of Wisconsin and James Stine of Lehigh University prepared the SimpleScalar problems in the instructor’s manual, and Todd also authored the SimpleScalar User’s Guide.
Finally, I would like to thank the many people responsible for the publication of the book, all of whom did their usual excellent job. This includes the staff at Pearson Education, particularly my editor Tracy Dunkelberger, her assistant Carole Snyder, and production managers Kayla Smith-Tarbox and Pat Brown. I also thank Shiny Rajesh and the production staff at Integra for another excellent and rapid job. Thanks also to the marketing and sales staffs at Pearson, without whose efforts this book would not be in your hands.
This page intentionally left blank
ABOUT THE AUTHOR
Dr. William Stallings has made a unique contribution to understanding the broad sweep of technical developments in computer security, computer networking and computer architecture. He has authored 17 titles, and counting revised editions, a total of 42 books on various aspects of these subjects. His writings have appeared in numerous ACM and IEEE publications, including the Proceedings of the IEEE and ACM Computing Reviews.
He has 10 times received the award for the best Computer Science textbook of the year from the Text and Academic Authors Association.
In over 30 years in the field, he has been a technical contributor, technical manager, and an executive with several high-technology firms. He has designed and implemented both TCP/IP-based and OSI-based protocol suites on a variety of computers and operating systems, ranging from microcomputers to mainframes. As a consultant, he has advised government agencies, computer and software vendors, and major users on the design, selection, and use of networking software and products.
He created and maintains the Computer Science Student Resource Site at WilliamStallings.com/StudentSupport.html. This site provides documents and links on a variety of subjects of general interest to computer science students (and professionals). He is a member of the editorial board of Cryptologia, a scholarly journal devoted to all aspects of cryptology.
Dr. Stallings holds a PhD from M.I.T. in Computer Science and a B.S. from Notre Dame in electrical engineering.
This page intentionally left blank
CHAPTER
READER’S AND INSTRUCTOR’S GUIDE
0.1 Outline of the Book
0.2 A Roadmap for Readers and Instructors
0.3 Why Study Computer Organization and Architecture?
0.4 Internet and Web Resources
Web Sites for This Book
Computer Science Student Resource Site
Other Web Sites
This book, with its accompanying Web sites, covers a lot of material. In this chapter, we give the reader an overview.
0.1 OUTLINE OF THE BOOK
The book is organized into five parts:
Part One Overview: Provides an overview of computer organization and architecture and looks at how computer design has evolved.
Part Two The Computer System: Examines the major components of a computer and their interconnections, both with each other and the outside world. This part also includes a detailed discussion of internal and external memory and of input/output (I/O). Finally, the relationship between a computer’s architecture and the operating system running on that architecture is examined.
Part Three Arithmetic and Logic: This part begins with a chapter that reviews number systems. Chapter 10 is an extended discussion of computer arithmetic. Chapter 11 is a survey of digital logic.
Part Four The Central Processing Unit: Examines the internal architecture and organization of the processor. This part looks at the instruction set architecture. The remainder of the part deals with the structure and function of the processor, including a discussion of reduced instruction set computer (RISC) and superscalar approaches.
Part Five Parallel Organization: Deals with parallel organization, including symmetric multiprocessing, clusters, and multicore architecture.
Part Six The Control Unit: Discusses the internal structure of the processor’s control unit and the use of microprogramming.
A number of online chapters and appendices at this book’s Web site cover additional topics relevant to the book.
This text is intended to acquaint you with the design principles and implementation issues of contemporary computer organization and architecture. Accordingly, a purely conceptual or theoretical treatment would be inadequate. 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 x86 family and the ARM family. These two systems together encompass most of the current computer design trends. The Intel x86 architecture is essentially a complex instruction set computer (CISC) with some RISC features, while the ARM is essentially a RISC. Both systems make use of superscalar design principles, and both support multiple processor and multicore configurations.
0.2 A ROADMAP FOR READERS AND INSTRUCTORS
This book follows a top–down approach to the presentation of the material. As we discuss in more detail in Section 1.2, a computer system can be viewed as a hierarchical structure. At a top level, we are concerned with the major components
of the computers: processor, I/O, memory, and peripheral devices. Part Two examines these components and looks in some detail at each component except the processor. This approach allows us to see the external functional requirements that drive the processor design, setting the stage for Parts Three and Four. Part Three looks at the arithmetic and logic component of the processor in detail. Then Part Four examine the processor in great detail. Because we have the context provided by Part Two, we are able, in Part Four, to see the design decisions that must be made so that the processor supports the overall function of the computer system. Next, in Part Five, we examine systems with multiple processors, including clusters, multiprocessor computers, and multicore computers. Finally, Part Six looks at the control unit, which is at the heart of the processor. Again, the design of the control unit can best be explained in the context of the function it performs within the context of the processor.
0.3 WHY STUDY COMPUTER ORGANIZATION AND ARCHITECTURE?
The IEEE/ACM Computer Science Curriculum 2008, prepared by the Joint Task Force on Computing Curricula of the IEEE (Institute of Electrical and Electronics Engineers) Computer Society and ACM (Association for Computing Machinery), lists computer architecture as one of the core subjects that should be in the curriculum of all students in computer science and computer engineering. The report says the following:
The computer lies at the heart of computing. Without it most of the computing disciplines today would be a branch of theoretical mathematics. A professional in any field of computing should not regard the computer as just a black box that executes programs by magic. All students of computing should acquire some understanding and appreciation of a computer system’s functional components, their characteristics, their performance, and their interactions. Students need to understand computer architecture in order to make best use of the software tools and computer languages they use to create programs. In this introduction the term architecture is taken to include instruction set architecture (the programmer’s abstraction of a computer), organization or microarchitecture (the internal implementation of a computer at the register and functional unit level), and system architecture (the organization of the computer at the cache and bus level). Students should also understand the complex trade-offs between CPU clock speed, cache size, bus organization, number of core processors, and so on. Computer architecture also underpins other areas of the computing curriculum such as operating systems (input/ output, memory technology) and high-level languages (pointers, parameter passing).
Another publication of the task force, Computer Engineering 2004 Curriculum Guidelines, emphasized the importance of Computer Architecture and Organization as follows:
Computer architecture is a key component of computer engineering and the practicing computer engineer should have a practical understanding of this topic. It is concerned with all aspects of the design and organization of the central processing unit and the integration of the CPU into the computer system itself. Architecture extends upward into computer software because a processor’s architecture must cooperate with the operating system and system software. It is difficult to design an operating system well without knowledge of the underlying architecture. Moreover, the computer designer must have an understanding of software in order to implement the optimum architecture.
The computer architecture curriculum has to achieve multiple objectives. It must provide an overview of computer architecture and teach students the operation of a typical computing machine. It must cover basic principles, while acknowledging the complexity of existing commercial systems. Ideally, it should reinforce topics that are common to other areas of computer engineering; for example, teaching register indirect addressing reinforces the concept of pointers in C. Finally, students must understand how various peripheral devices interact with, and how they are interfaced to a CPU.
[CLEM00] gives the following examples as reasons for studying computer architecture:
1. Suppose a graduate enters the industry and is asked to select the most costeffective computer for use throughout a large organization. An understanding of the implications of spending more for various alternatives, such as a larger cache or a higher processor clock rate, is essential to making the decision.
2. Many processors are not used in PCs or servers but in embedded systems. A designer may program a processor in C that is embedded in some real-time or larger system, such as an intelligent automobile electronics controller. Debugging the system may require the use of a logic analyzer that displays the relationship between interrupt requests from engine sensors and machinelevel code.
3. Concepts used in computer architecture find application in other courses. In particular, the way in which the computer provides architectural support for programming languages and operating system facilities reinforces concepts from those areas.
As can be seen by perusing the table of contents of this book, computer organization and architecture encompasses a broad range of design issues and concepts. A good overall understanding of these concepts will be useful both in other areas of study and in future work after graduation.
0.4
AND WEB RESOURCES
There are a number of resources available on the Internet and the Web that support this book and help readers keep up with developments in this field.
Web Sites for This Book
Three Web sites provide additional resources for students and instructors. We maintain a Companion Web site for this book at http://williamstallings. com/ComputerOrganization. For students, this Web site includes a list of relevant links, organized by chapter, and an errata list for the book. For instructors, this Web site provides links to course pages by professors teaching from this book.
There is also an access-controlled Premium Content Web site that provides a wealth of supporting material, including additional online chapters, additional online appendices, a set of homework problems with solutions, copies of a number of key papers in this field, and a number of other supporting documents. See the card at the front of this book for access information.
Finally, additional material for instructors is available at the Instructor Resource Center (IRC) for this book. See Preface for details and access information.
Computer Science Student Resource Site
I also maintain the Computer Science Student Resource Site, at ComputerScienceStudent.com. The purpose of this site is to provide documents, information, and links for computer science students and professionals. Links and documents are organized into six categories:
• Math: Includes a basic math refresher, a queuing analysis primer, a number system primer, and links to numerous math sites.
• How-to: Advice and guidance for solving homework problems, writing technical reports, and preparing technical presentations.
• Research resources: Links to important collections of papers, technical reports, and bibliographies.
• Miscellaneous: A variety of other useful documents and links.
• Computer science careers: Useful links and documents for those considering a career in computer science.
• Humor and other diversions: You have to take your mind off your work once in a while.
Other Web Sites
Numerous Web sites provide information related to the topics of this book. The Companion Web site provides links to these sites, organized by chapter.
CHAPTER
INTRODUCTION
1.1 Organization and Architecture
1.2 Structure and Function Function Structure
1.3 Key Terms and Review Questions
Another random document with no related content on Scribd:
The Project Gutenberg eBook of The terrors of the upper air
This ebook is for the use of anyone anywhere in the United States and most other parts of the world at no cost and with almost no restrictions whatsoever. You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included with this ebook or online at www.gutenberg.org. If you are not located in the United States, you will have to check the laws of the country where you are located before using this eBook.
Title: The terrors of the upper air
Author: Frank Orndorff
Illustrator: Frank R. Paul
Release date: April 27, 2024 [eBook #73477]
Language: English
Original publication: New York, NY: Experimenter Publishing Company, 1928
Credits: Roger Frank and Sue Clark
*** START OF THE PROJECT GUTENBERG EBOOK THE TERRORS OF THE UPPER AIR ***
“They got poor Dexter. He went first, after we had enlarged the hole, and before he had dropped five hundred feet, the monsters were after him. He was helpless in the parachute.”
Our knowledge of the upper air is very limited. The highest point a human being has ever ascended in a free balloon is about seven miles. What exists beyond this, we do not know. Our new author presents a very unusual, as well as complex situation, with a typical O. Henry ending. As to ourselves, we enjoyed the story hugely and the chances are that you will too.
The Terrors of the Upper Air
by Frank Orndorff
Pemberton, the Great Detective, renowned as never having failed to get his man, spoke to the Secretary of the President of the State Fair, and passed on to the President’s office door marked “Private.” He entered without knocking.
“Well! What happening is responsible for this visit?” The President sprang up and grasped Pemberton’s hand and pulled a chair out for him. “You are not in the habit of calling on me lately except on business. Who are the unlucky people at the Fair that you want? For my guess is that you are after some poor birds.”
Pemberton sat down and placed his hat on the President’s desk. “You are right to call them birds. I am after your human birds, and they can’t particularly be called ‘poor’—not now, anyhow.”
“What!” exclaimed the President, as he half rose in his seat, “surely you are not after Kidwell and Dexter, the aviators who are flying for the Fair.”
“The very two men I am after.”
“But what have they done? It must be something serious.”
“It is serious. You remember the Windsor Bank Robbery of over a week ago, where the cashier was killed and nearly a half a million dollars, mostly in large bills was stolen? The two men who did the job escaped in an auto. They were chased to a large wooded tract just about nightfall. When the pursuers closed in, they found the car but the men and the money were gone.”
“I remember that and also the mystery of their escape from the hundreds of men that surrounded the woods.”
“They did not escape through this fence of men, but over them. As soon as I had gone over the ground, I found tracks of where an aeroplane had made a short run in a break in the woods and could easily have shot upwards above the trees and away. The place was far enough from the edge of the woods, to enable the roar of the motor to go unheard as the two men fled away in the night.
“The run to the woods and the flight in the aeroplane was most likely planned ahead by the two men and would have remained undiscovered had it not been for a mark made in the soft ground by two small cuts in one of the aeroplane tires. It was one chance in a thousand that we ever found the aeroplane tracks and one in a million that it left the print of these two small cuts in the tire’s tread. Hundreds of aeroplanes are being driven across that part of the country each day and it would have been practically impossible to find the one that made the track if it had not been for the two small cuts. My men have informed me that the aeroplane of Kidwell and Dexter has a tire on it with two small cuts the same size and distance apart as the two marks left in the woods. I have just arrived and we expect to arrest the two aviators within the next few minutes. I thought I would notify you first, as I realize it will stop your exhibition flight for the Fair.”
“If these two men are murderers and robbers, as you state, I want you to arrest them at once—exhibition flight or no exhibition flight. You will have to hurry or wait until—listen—” The President broke off and turned his head to one side to hear better.
A roar of a multitude cheering came to the two listening men—the huge crowd at the Grand Stand were splitting the air with deafening cheers for something. “They are up and off.” The President continued after listening awhile. “You will have to wait until they come down. They are up to beat the world’s highest altitude record. Here is one of our advertisements for today. Read it.”
Pemberton took the paper that was handed him and read the following:
“WILL TRY TO BEAT THE WORLD’S HIGHEST ALTITUDE RECORD”
STATE FAIR—AUGUST 25, 19—
Kidwell and Dexter—the world’s most daredevil aviators will try to beat the world’s highest altitude record for an aeroplane. They will use the latest type of aeroplane with new wing devices for climbing and flying in the rarefied air of miles above the earth. They will carry an extra supply of oxygen. They will have
the latest thing in wireless telephone instruments and will be in constant communication with the receiving station established in front of the Grand Stand. To the receiving instrument will be attached a sound magnifier and those within a radius of several hundred feet can listen to the account from the aviators’ own lips as they circle up—up—up.
Don’t Forget the Place and Date
Pemberton handed the paper back and inquired, “How long will it take them to make the flight?”
“About two or three hours is all they figured they would need,” he answered.
Pemberton decided to go to the receiving station to listen, and the President went with him.
The two men made their way across the crowded Fair Grounds until they came in front of the large Grand Stand. Here a crowd of several thousand people were jammed around a platform on which were a few men, and a table of instruments, the largest part of which were four huge phonograph-like horns that faced in four directions. They made their way through the crowd and had just climbed to the platform, when a voice issued from the horns. The words were:
“Have just reached three thousand feet.”
Looking upwards, Pemberton could see a speck circling above and rapidly growing smaller. It was the aeroplane winging its way ever higher and higher. He leaned over to the President, “How is it we can hear their voices and can not hear the roar of the motor? On the ground it was impossible to hear a voice because of the deafening roar of an aeroplane motor.”
The President leaned over and tapped one of the men on the shoulder, who was tinkering with the instrument, and said, “Billy, tell Mr. Pemberton here about the wireless telephone—tell him why one can hear a voice from above and yet not hear the roar of the motors.”
Billy dropped into a chair next to Pemberton and keeping one eye on the instrument, explained:
“Kidwell and Dexter are using the same kind of wireless telephone instruments that our aviators in France had begun to use when the war ended, to communicate with each other and with headquarters. You know sound is vibration of the air and travels in waves and in a straight line unless turned aside by something. The aviator’s instrument is like a helmet and covers most of his head. The receivers are flat and lie over his ears. The outside sound is deadened by the padding in the helmet and it was found that it would be necessary for the padding to cover most of the lower jaw to kill the outside sound. The mouth-piece, the part they talk into, is fastened directly in front of the mouth. It is padded to stop the outside sound. Only a tube-like opening directly even with the person’s mouth is left unpadded. There are three or four small holes in the tube and when the person talks, his voice is thrown straight through the small openings and makes the instrument work while other sounds pass by as the waves do not get a straight entrance to the diaphragm.”
“Both the receivers and the mouth-piece have wires running to a plug in the side of the aeroplane which connects with the batteries and instrument that send the wireless waves in all directions and reach us; they also catch any that we should send and transfer it to speech when it reaches the ears. Instead of the usual receiving instrument, we have hooked on a sound magnifier here, so that everybody can hear directly. Now the very—”
“One mile up and everything is running fine.”
The voice of one of the men from the speck above spoke from the horns. A cheer greeted the announcement.
“Who is doing the talking?” Pemberton asked.
“Kidwell will do all the talking because it is he who is equipped with the long distance sending and receiving apparatus. Dexter can talk with Kidwell and Kidwell can talk with Dexter by changing the plug at the side of the machine, so he is directly connected with Dexter. Dexter is the pilot in the rear seat and will drive unless something happens. If something should happen, Kidwell can drive as they have double controls.”
“Hey, below! We are having fun up here chasing toy balloons. Those that have been let loose on the Fair Grounds have reached this far up. There are twenty or thirty in sight. We have run down three or four. One was thrown back by the propeller’s draft and hit Old “Dex” on the head and busted. He would have jumped out of his seat if he were not tied down with a safety belt. Thought part of the machinery had hit him, I guess. We are climbing in circles and staying over the Fair Grounds as nearly as we can. The hand on our instrument is gradually crawling near two miles and we can begin to tell it is getting very cold. We feel sorry for you poor land mortals below sweating in that 100 degrees in the shade. But say, ‘you don’t have to stay in the shade’—Ha, Ha!”
The sound of Kidwell’s laughter from two miles above roared through the horns. It ceased and no other sound came from above for several minutes.
“Got another balloon; caught it alive this time; going to tie my pipe to it and drop it overboard. The pipe will pull it down. Tell the kids down there I will give five dollars to the one who gets it and I will wring their necks if any of them busts my pipe. Here she goes—”
Cheers and laughter greeted this last announcement and many small boys jammed in the crowd began to crowd and squirm frantically to get out into the center field where they could watch for Kidwell’s pipe pulling a toy balloon down.
“You below! We are going to have trouble in just a minute. Saw several balloons above us snatched and rushed east at a speed that makes us look like a snail. It’s one of those terrific wind currents that different persons have discovered two or three miles up. We will be O. K. when we get in it, but going from slow to fast air is going to give us some rough riding. We are starting; I can feel our old machine beginning to pitch. Here we go!— God, we are pitching and spinning like a leaf. We are on our tail—now we are upside down. Over we go sideways—now we are level—whew, we just made a complete flip-flop. It’s a wonder we hold together—we are rocking and pitching like a row boat on a stormy ocean.
“We are getting up in the main current and don’t pitch so much. It is all I can do to hold my dinner down. I’m sea-sick—we are heading
west, but I think we are losing several miles a minute as this terrific air current drifts us east.”
A deadly hush fell on the crowd below as they pictured the aeroplane being tossed and pitched about in one of the mighty air currents that are found miles above the earth. They could see the two men fighting to keep their machine right side up, as they fought through the eddies and whirls at the edge of the current and into the steady but fast moving air of the center. When Kidwell announced that they had made it, a mighty cheer went up. Several minutes passed and no sound came from the men miles above—then——
“Hurrah for the Liberty Motor—we just had another fight to get out of the big current and are now in still air above it. We were pitched and flung about, upside down and every which way, just as when we entered it. Our Motor did not miss a lick. Old “Dex” got sick. I saw him gulping and raise his helmet and lean over, but nothing happened. Now we are riding smoothly. We are heading straight west instead of circling so as to gain the distance we were carried backwards in the big air current. It is getting cold. We are using oxygen from our tanks as the air is mighty thin here—Dex has just called my attention to our instrument—what do you reckon she reads?—whoop—she has touched it. She’s reached thirty thousand feet. We’ll make it. We’ll break that old world’s altitude record.”
A roar that shook the Grand Stand went up from the listening crowd below. For ten minutes they cheered and flung things in the air in their excitement. A few more minutes and the world’s highest altitude record would belong to America once more. The cheering died down and then broke out afresh.
“What is the world’s record?” Pemberton leaned over and shouted above the din into the president’s ear.
“A little less than thirty-five thousand feet,” the President answered in one of the partly quiet spells of the crowd.
“Thirty-one thousand” came from the horns,—only those right against them could hear, but they began to relay the news. “Thirtyone thousand.” Another deafening cheer rang out. The crowd became silent as the President raised his hand for silence and pointed to the horns.
“Thirty-two thousand and Old Dex grinning like a frog.”
This time only a laugh from the crowd greeted the announcement. They would hold their cheers for the last as they wanted to hear all now.
“It’s just about there—now it’s closer—just a little more—near— nearer—— Gee, it moves slowly—just ready to touch—now it touches—whoopee—it’s over—we have reached the world’s altitude record—now we have passed it.”
The Grand Stand roared and shook as the crowd below let loose. Hats flew high in the air, men thumped each other like boys. Once more the world’s altitude record belonged to America—to the United States—brought to it by the two dauntless aviators, far out of sight in the vast space above. Those in the Grand Stand began to stamp and shout in unison and stopped only when the stand threatened to break under the strains of the thousands of thumping feet. At the rear of the mass of people, a boy with a toy balloon struggled to get through to the platform.
“Hey, kid, look out or you’ll get hurt crowding in like that,” a man addressed him.
“I caught the pipe,” the boy cried as he held aloft a pipe tied to the balloon string.
“Kidwell’s pipe—Kidwell’s pipe”—the man shouted as he gathered the boy up and held him above the crowd’s head. From hand to hand they passed the boy to the platform, where the President of the Fair met him and led him to the front of the platform where the boy held up the toy balloon with the pipe tied to it. The boy was still panting, for he had caught the pipe nearly a quarter of a mile away and had run all the way back to the crowd, while other boys chased him. The President took a five dollar bill from his pocket and gave it to the boy and took possession of the pipe The boy struck through the crowd, headed for the refreshment stands, while the President returned to his seat.
“Forty thousand feet up and cold as fifty North Poles.”
The people became quiet with awe. Not satisfied with breaking the world’s altitude record, these two daredevils were steadily
climbing higher and higher Forty thousand feet—miles high—how far would they go?
“We have just noticed a queer color of the air just a short way to our west, although we can hardly call it color. It might be just our imagination; anyway Dex has headed the machine in that direction— yes we notice the difference more as we get closer—turn her Dex— turn her— My God it’s a whirlwind—loop her back, Dex—turn——”
The last, regarding turning the machine, came from the horns in a shout and must have been meant for Dexter It broke off suddenly as Kidwell must have changed the plug from below to connect with Dexter.
Thousands of eyes unconsciously looked upward, although all knew that it was impossible to see to the great height the aeroplane had attained. But all realized that something serious was happening miles above. What had happened? Would the aeroplane come flying down from above and land a shattered wreck?
Minutes passed and no voice was heard through the horn. The suspense became unbearable. Several more minutes passed and at last came—
“Hello, below,—we thought we were gone that time. We ran into a whirling draft of air of cyclone speed. Our machine was caught in it and we were pitched over and over like a feather, whirling, tossing, and tumbling. We were flung up—up—and up. We don’t know how far up we are now, because we were carried upward for many minutes at many miles a minute. Our instrument only registers sixty thousand feet and the hand reached that mark long before we were pitched out of the whirling mass and into still air. The current seems to come up and then turn east and we were flung to the top side. We must be fifteen or twenty miles high—way above any height we dreamed a person could fly. Our motor does not run as smoothly as it did below, but it is doing fairly well. We still have to use our own supply of oxygen. The movements of the machine are rather slow and sluggish. It might be that we are flying in air hurled up in that mighty up-rushing funnel of air from below. We can not understand it. We are circling about, getting our nerve back to make a dive for the
earth. If we get through the high eastward current of air and miss the upward whirlwind, we will be O. K. If we hit the upward whirlwind, we will be flung back like a leaf. We can feel the intense cold through all our furs. It must be fifty degrees below zero. Nothing but space, space, space, as far as you can see and in every direction. You feel like loosening, your belt, stepping on the edge of the machine and stepping off into—nothing—you feel as though there were no world —no God—No——”
The voice broke off and then continued with a note of excitement in it.
“We have made a discovery; there are clouds up here—Dex just pointed several out to me and we are headed for them. They seem very dense as we get nearer.”
For several minutes the voice stopped and those below talked in suppressed excitement. They were past the cheering stage now. What had happened miles above the earth had made them curious and started them thinking. Then the voice came, quivering with a tone of excitement.
“People, below! I am going to make a statement to you that will seem unbelievable, a statement that will upset all past theories of the upper air. If I were not sure of bringing down proofs of my statements, I would not make it and I don’t even ask you to believe it, until we come back.
“People, below—there is vegetable and animal life here. We are now flying above a floating island of vegetable substance while around us and above are hundreds of other floating islands of the same substance. I have managed to catch a small handful of the substance as it floated in the air between the larger bodies of the same thing.
“It is nearly transparent, but has a pale greenish color It is spongy and tough, being made up of a rubber-like material full of thousands of small gas pockets. It must be this gas that keeps it afloat at this great height. It grows on long rope-like branches like sea-kelp or some kind of moss. What we took for clouds were great masses of this plant matted together and floating about. I believe we could walk on these islands, but it would be impossible to land our aeroplane for it would sink too deep to get it out again.
“We have seen a small bat-like animal fly from one island to another. Another of the same kind of creatures is flying alongside us and keeps turning its head to watch us as though it wonders what we are. I believe it is as much surprised to see us as we are to see it. Dex has just notified me that he will try to run it down and wants me to catch or kill it. We must bring down proofs or we would never dare tell of such things as are up here. Here we go—we are after the batlike animal. Zip!—the blamed little thing is gone; it was just fooling along with us and when we whirled to reach it, it shot away like a bullet. They are too speedy for us to run down. I was close enough to see that it was nearly the size and shape of a bat, except that it had a head like a bird with large owl-like eyes, and had a beak instead of a mouth with teeth. It was of the same pale sickly green like the plants we have found.
“Dex has spied something else ahead and is pointing for me to see but I fail to make it out. Now I see it. It is something long twisting through the air. It is turning and coming this way. It is another animal, or a reptile for it is more like a snake. No, not like a snake either, for it is about ten feet long and flat as can be. Its head is also formed with a beak. It looks like a huge ribbon floating through the air. It has turned and is flying above and to one side of us, looking down at us while it winds its way along. If we can get within striking distance, I will take a swipe at it with a wrench. I would like to bring it down— Look out, Dex—now—hold her steady.”
The last came in a shouted command and must have been meant for Dexter, then——
“That queer snake-like thing turned and in a flash had straightened out in a line and shot down on us like a bullet. It hit the top of our right wing and went through as though the wing were a spider web. Then it struck one of our stay wires and was split long ways for a foot or more. It clung to the wire, thrashing about, a blood of that pale greenish color oozing out. When I was ready to go out on the wing and try to get it, it fell on the lower plane and was blown off. It fell below to the plant island over which we are flying now. If it had struck either of us, it would have been death. A short distance more and we will make the dive for earth as our oxygen supply is getting
low I have been catching stray pieces of the plants of which the islands are made and have a bunch packed in the bottom of my cockpit. There is also a large bunch caught in the wires of our left wing and several small bunches caught in other places. These might hold fast until we get down. I have been wondering if the change of pressure on the plant and animals—if we can catch any animals to bring down—will cause them to contract. The effect on them should be just the opposite of the effect on the fish that have been brought up from two miles or more under the sea; when they came up, the pressure was so much less that some swelled up and exploded. I believe these animals would be pressed together more if brought to the denser air of the earth’s surface. This plant up here might be made good use of below at some future time and if—of all the sights —what monsters! What fierce fighting monsters. Look at the great gashes they are tearing in each other. They can’t last.
“Oh, I forgot, you below—we just turned a half circle around the end of a medium sized floating island and have come upon one of the most awful battles between two of the biggest and fiercest of monsters. One is like a large flying alligator, except that it has a huge beak and large bat-like wings. The other is shaped like an octopus, but has flat arms and two large balloon-like appendages on its back. It has a hellish beak. They are closed in one biting, clawing and choking mass. We are circling them and watching. The flying alligator just laid open one of the devil-fish of the air’s balloons. It shrank as though it were full of gas. Now they are whirling on the air so fast you can hardly tell what is happening. The alligator has lost the use of one of its wings. The octopus has wrapped several of its arms around it. They are starting to sink. They’re dropping, two of the arms, bitten off. Everything up here is that sickly green, both monsters are that color and they are bleeding the green blood —if it is blood. They are now covered with gashes all over their bodies. They can’t last much longer. There goes the other balloon. It shrinks —now they are falling.
“They don’t stop fighting. We are following them down and still circling around them. The two fighting air demons have fallen on the
big island below us. They are hardly able to move. The alligator devil is now on top and rending the octopus to shreds. Its days are over. The flying alligator—for I don’t know what else to call it—is victor, but it will never be able to fly again. One wing is completely torn in shreds and the other is not much better. Its body is full of big wounds. The din of their screams and clashing of their beaks must have been awful. Where they came from or what they were fighting about, we do not know. It was one of the most terrific and most aweinspiring sights, man ever witnessed.
“The flying alligator has risen on its hind legs and is trying to lunge itself into the air, but it can only flutter like a broken-winged bird. It is giving out its cry, as we can see by the motion of its beak.
“Dex shut off the motor for an instant and drifted close over its head. It uttered a piercing scream like a thousand wild cat whistles, and lunged up for us. I hate to think what would have happened if it had been able to fly. I believe it would have rent us in pieces in a second. We are leaving here right now, for Dex has pointed out another flying alligator about a mile away, which is coming this way. It must be answering the wounded one’s cries. It is traveling fast and coming from the north. We can see its giant, bat-like wings beating the air and it rises and falls at each stroke. We are speeding westward and as soon as we reach the edge of this extra large floating island over which we are flying, we will dive for the earth. We can not see the edge, but it cannot be over a mile or so. We have left the wounded flying alligator about a half mile back, and the other monster has already reached it and has circled above it once.
“God, it has turned and is headed after us, its huge wings beating faster than before. We must reach the edge and dive, for it travels twice as fast as our sluggish-acting machine. I am not scared, for I can see the edge about two miles ahead and we will reach it before the demon can overtake us. Another has dropped from above where the wounded alligator is and it, also, is now headed after us. Miles above the earth and being chased by two hideous monsters. Have you ever noticed birds flying? When they beat their wings downwards, they not only go forward, but partly upward as well, and when they raise their wings for another stroke, they sink a little
instead of keeping a straight course ahead. That is the way these demons fly. Dex is giving our machine all it will take.
“The two demons are going fast, but we will reach the edge before they can catch us. God help us, another monster and straight ahead. We can not go that way and must turn south or north. No, not north for I see two coming from that direction. We are nearly surrounded and our only hope is south. I see the edge south, but it is a mile farther away than west. But we will make it. I don’t see any of the demons coming from that direction. Our machine is roaring at full speed, but we are not making over fifty or sixty miles in this rarefied air. The demons of this upper air are flying twice as fast and now there are nearly a dozen close on our trail and swiftly gaining.... We are near the edge and our danger is over. A minute more and we would have been lost, for now there are two monsters in front of us. We are surrounded, but we will reach the edge and will head down like a bullet before they can get near enough to head us off. Their screams are bringing other monsters from all directions.
“Just passed one of those hideous flying devil-fish and see another ahead and above us. We are just at the edge and are tipping down for our long dive. Will be with you in a few—— Dex, Dex, look out for the devil-fish. For God’s sake, look, Dex—— Oh, God, too late— We are done. Our propeller is shattered, we are falling. Look out below— No, we have fallen on the edge of the island. We are tearing through. No we have stopped. God, we are in a fix. The devilfish flung itself at us and into our propeller and wrecked it and blocked the controls and we fell straight down. We are within a few hundred feet of the edge, the weight of the machine has sunk us until we rest in a sloping crater about fifty feet deep. The monsters are arriving and flying in circles above us. Our motor is quiet and when we raise our receivers, the screams and snapping of their giant beaks almost deafen us. Our only hope now is to reach the edge and trust ourselves to our safety parachutes.”
For several minutes the horns were quiet and the people jammed around them listening for further word from the two men in the void above. They whispered together in low under-tones and every minute or so their eyes traveled upward in an attempt to pierce the
blind of the miles distance. But in vain. At last—it seemed hours, though it was only a few minutes—the voice came again.
“We took our parachutes from their holders on the side of the machine and started up to the top of the sink-hole we are in. The monsters began to come closer as we neared the top and one made a dive for us, so we retreated to the machine. They seem to be afraid to come into this pit we are in. We found a place on one side of the pit where the vegetable has been pulled until it has pulled apart and we can see below. We are going to this hole now and enlarge it sufficiently to enable us to drop through—all is clear below—so good-bye, but watch for us to come sailing down soon. We are carrying oxygen tanks with us to breathe.”
The voice ceased and the crowd began to watch above for any specks that might turn out to be the two men and their parachutes. Many minutes passed, then the voice came, a voice filled with a tone of despair and terror.
“They got poor Dexter He went first, after we had enlarged the hole, and before he had dropped five hundred feet a dozen of the monsters were after him. Helpless in the parachute, they dived on him and dragged him up to the top of the island and tore him to shreds. Now they are screaming and snapping their beaks above this pit and are swooping nearer and nearer. Their taste of blood seems to have made them wilder. I will fight them from the cockpit and if I can hold out until night, I might drop through the hole and escape in the darkness. I have broken a spar loose for a club. They are coming closer I struck at that one. It just missed my head. They are gathering in a bunch. They are diving for me in one mass. I’m lost—Good-bye.”
A shriek of a man in mortal agony and terror rang out in the air, followed by a shriek from the crowd. Then all was still. The people knew all was over in the far upper air. Men stood gazing upward, ghastly white, while women buried their faces in their hands and wept.
A dull thud was heard at the far side of the infield and people began to gather there on a run. A hole showed where something had
fallen with enough force to bury itself. Hurriedly digging, they unearthed an oxygen tank, one of the tanks that Kidwell and Dexter had taken up with them. A cry from some people as they pointed aloft drew thousands of eyes in that direction. Fluttering and falling, something was coming down. Several hands grabbed it as soon as it came within reach. One uttered a cry and let go. He held up his hands in horror. They were wet with fresh blood.
A broken and torn part of an aeroplane wing, spattered with red blood, fell. Kidwell and the aeroplane must have been torn to pieces by the demons of the far upper air, and the tank and pieces of the plane scattered over the edge of the floating vegetable island, must have fallen to earth.
Another shout and once more all looked aloft. The air was full in all directions with thousands of fluttering pieces that looked like paper. When they fell among the crowd a shout of surprise went up.
“Money—Money—One dollar bills.”
Over the ground for miles around the Fair Grounds there fell a shower of one dollar bills. This was the last thing ever heard or seen of the two men and the aeroplane.
A few weeks later Pemberton and the President of the State Fair were talking in the President’s office. The President spoke:
“I have had two different planes up since Kidwell and Dexter were lost. The men went armed with shot guns and prepared for trouble. They were unable to find any upward current of air and they cruised all around in search of it. I am informed, though, that such a current would not necessarily always be in the same place, else it might stop altogether, just like winds near the earth. I have given up hope of anybody reaching the scene of the awful tragedy above.”
“If there ever was an awful tragedy above,” Pemberton added. The President looked at him in blank surprise.
“What?”
“I say if there ever was an awful tragedy above—if Kidwell and Dexter ever did get over two or three miles high.”
“What? Don’t you think that Kidwell and Dexter were killed by the monsters many miles above the earth, as they described? Why do you think they weren’t?”
