Fundamentals of Dependable Computing for Software Engineers

Fundamentals of Dependable Computing for Software Engineers

Author: John Knight

Publisher: CRC Press

Published: 2012-01-12

Total Pages: 438

ISBN-13: 1439862559

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Fundamentals of Dependable Computing for Software Engineers presents the essential elements of computer system dependability. The book describes a comprehensive dependability-engineering process and explains the roles of software and software engineers in computer system dependability. Readers will learn: Why dependability matters What it means for a system to be dependable How to build a dependable software system How to assess whether a software system is adequately dependable The author focuses on the actions needed to reduce the rate of failure to an acceptable level, covering material essential for engineers developing systems with extreme consequences of failure, such as safety-critical systems, security-critical systems, and critical infrastructure systems. The text explores the systems engineering aspects of dependability and provides a framework for engineers to reason and make decisions about software and its dependability. It also offers a comprehensive approach to achieve software dependability and includes a bibliography of the most relevant literature. Emphasizing the software engineering elements of dependability, this book helps software and computer engineers in fields requiring ultra-high levels of dependability, such as avionics, medical devices, automotive electronics, weapon systems, and advanced information systems, construct software systems that are dependable and within budget and time constraints.


Book Synopsis Fundamentals of Dependable Computing for Software Engineers by : John Knight

Download or read book Fundamentals of Dependable Computing for Software Engineers written by John Knight and published by CRC Press. This book was released on 2012-01-12 with total page 438 pages. Available in PDF, EPUB and Kindle. Book excerpt: Fundamentals of Dependable Computing for Software Engineers presents the essential elements of computer system dependability. The book describes a comprehensive dependability-engineering process and explains the roles of software and software engineers in computer system dependability. Readers will learn: Why dependability matters What it means for a system to be dependable How to build a dependable software system How to assess whether a software system is adequately dependable The author focuses on the actions needed to reduce the rate of failure to an acceptable level, covering material essential for engineers developing systems with extreme consequences of failure, such as safety-critical systems, security-critical systems, and critical infrastructure systems. The text explores the systems engineering aspects of dependability and provides a framework for engineers to reason and make decisions about software and its dependability. It also offers a comprehensive approach to achieve software dependability and includes a bibliography of the most relevant literature. Emphasizing the software engineering elements of dependability, this book helps software and computer engineers in fields requiring ultra-high levels of dependability, such as avionics, medical devices, automotive electronics, weapon systems, and advanced information systems, construct software systems that are dependable and within budget and time constraints.

Foundations of Dependable Computing

Foundations of Dependable Computing

Author: Gary M. Koob

Publisher: Springer Science & Business Media

Published: 1994-09-30

Total Pages: 224

ISBN-13: 0792394852

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Foundations of Dependable Computing: Paradigms for Dependable Applications, presents a variety of specific approaches to achieving dependability at the application level. Driven by the higher level fault models of Models and Frameworks for Dependable Systems, and built on the lower level abstractions implemented in a third companion book subtitled System Implementation, these approaches demonstrate how dependability may be tuned to the requirements of an application, the fault environment, and the characteristics of the target platform. Three classes of paradigms are considered: protocol-based paradigms for distributed applications, algorithm-based paradigms for parallel applications, and approaches to exploiting application semantics in embedded real-time control systems. The companion volume subtitled Models and Frameworks for Dependable Systems presents two comprehensive frameworks for reasoning about system dependability, thereby establishing a context for understanding the roles played by specific approaches presented in this book's two companion volumes. It then explores the range of models and analysis methods necessary to design, validate and analyze dependable systems. Another companion book (published by Kluwer) subtitled System Implementation, explores the system infrastructure needed to support the various paradigms of Paradigms for Dependable Applications. Approaches to implementing support mechanisms and to incorporating additional appropriate levels of fault detection and fault tolerance at the processor, network, and operating system level are presented. A primary concern at these levels is balancing cost and performance against coverage and overall dependability. As these chapters demonstrate, low overhead, practical solutions are attainable and not necessarily incompatible with performance considerations. The section on innovative compiler support, in particular, demonstrates how the benefits of application specificity may be obtained while reducing hardware cost and run-time overhead.


Book Synopsis Foundations of Dependable Computing by : Gary M. Koob

Download or read book Foundations of Dependable Computing written by Gary M. Koob and published by Springer Science & Business Media. This book was released on 1994-09-30 with total page 224 pages. Available in PDF, EPUB and Kindle. Book excerpt: Foundations of Dependable Computing: Paradigms for Dependable Applications, presents a variety of specific approaches to achieving dependability at the application level. Driven by the higher level fault models of Models and Frameworks for Dependable Systems, and built on the lower level abstractions implemented in a third companion book subtitled System Implementation, these approaches demonstrate how dependability may be tuned to the requirements of an application, the fault environment, and the characteristics of the target platform. Three classes of paradigms are considered: protocol-based paradigms for distributed applications, algorithm-based paradigms for parallel applications, and approaches to exploiting application semantics in embedded real-time control systems. The companion volume subtitled Models and Frameworks for Dependable Systems presents two comprehensive frameworks for reasoning about system dependability, thereby establishing a context for understanding the roles played by specific approaches presented in this book's two companion volumes. It then explores the range of models and analysis methods necessary to design, validate and analyze dependable systems. Another companion book (published by Kluwer) subtitled System Implementation, explores the system infrastructure needed to support the various paradigms of Paradigms for Dependable Applications. Approaches to implementing support mechanisms and to incorporating additional appropriate levels of fault detection and fault tolerance at the processor, network, and operating system level are presented. A primary concern at these levels is balancing cost and performance against coverage and overall dependability. As these chapters demonstrate, low overhead, practical solutions are attainable and not necessarily incompatible with performance considerations. The section on innovative compiler support, in particular, demonstrates how the benefits of application specificity may be obtained while reducing hardware cost and run-time overhead.

Foundations of Dependable Computing

Foundations of Dependable Computing

Author: Gary M. Koob

Publisher: Springer Science & Business Media

Published: 2007-08-19

Total Pages: 325

ISBN-13: 0585280029

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Foundations of Dependable Computing: System Implementation, explores the system infrastructure needed to support the various paradigms of Paradigms for Dependable Applications. Approaches to implementing support mechanisms and to incorporating additional appropriate levels of fault detection and fault tolerance at the processor, network, and operating system level are presented. A primary concern at these levels is balancing cost and performance against coverage and overall dependability. As these chapters demonstrate, low overhead, practical solutions are attainable and not necessarily incompatible with performance considerations. The section on innovative compiler support, in particular, demonstrates how the benefits of application specificity may be obtained while reducing hardware cost and run-time overhead. A companion to this volume (published by Kluwer) subtitled Models and Frameworks for Dependable Systems presents two comprehensive frameworks for reasoning about system dependability, thereby establishing a context for understanding the roles played by specific approaches presented in this book's two companion volumes. It then explores the range of models and analysis methods necessary to design, validate and analyze dependable systems. Another companion to this book (published by Kluwer), subtitled Paradigms for Dependable Applications, presents a variety of specific approaches to achieving dependability at the application level. Driven by the higher level fault models of Models and Frameworks for Dependable Systems, and built on the lower level abstractions implemented in a third companion book subtitled System Implementation, these approaches demonstrate how dependability may be tuned to the requirements of an application, the fault environment, and the characteristics of the target platform. Three classes of paradigms are considered: protocol-based paradigms for distributed applications, algorithm-based paradigms for parallel applications, and approaches to exploiting application semantics in embedded real-time control systems.


Book Synopsis Foundations of Dependable Computing by : Gary M. Koob

Download or read book Foundations of Dependable Computing written by Gary M. Koob and published by Springer Science & Business Media. This book was released on 2007-08-19 with total page 325 pages. Available in PDF, EPUB and Kindle. Book excerpt: Foundations of Dependable Computing: System Implementation, explores the system infrastructure needed to support the various paradigms of Paradigms for Dependable Applications. Approaches to implementing support mechanisms and to incorporating additional appropriate levels of fault detection and fault tolerance at the processor, network, and operating system level are presented. A primary concern at these levels is balancing cost and performance against coverage and overall dependability. As these chapters demonstrate, low overhead, practical solutions are attainable and not necessarily incompatible with performance considerations. The section on innovative compiler support, in particular, demonstrates how the benefits of application specificity may be obtained while reducing hardware cost and run-time overhead. A companion to this volume (published by Kluwer) subtitled Models and Frameworks for Dependable Systems presents two comprehensive frameworks for reasoning about system dependability, thereby establishing a context for understanding the roles played by specific approaches presented in this book's two companion volumes. It then explores the range of models and analysis methods necessary to design, validate and analyze dependable systems. Another companion to this book (published by Kluwer), subtitled Paradigms for Dependable Applications, presents a variety of specific approaches to achieving dependability at the application level. Driven by the higher level fault models of Models and Frameworks for Dependable Systems, and built on the lower level abstractions implemented in a third companion book subtitled System Implementation, these approaches demonstrate how dependability may be tuned to the requirements of an application, the fault environment, and the characteristics of the target platform. Three classes of paradigms are considered: protocol-based paradigms for distributed applications, algorithm-based paradigms for parallel applications, and approaches to exploiting application semantics in embedded real-time control systems.

Foundations of Dependable Computing

Foundations of Dependable Computing

Author: Gary M. Koob

Publisher: Springer Science & Business Media

Published: 2007-07-23

Total Pages: 272

ISBN-13: 0585273774

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Foundations of Dependable Computing: Models and Frameworks for Dependable Systems presents two comprehensive frameworks for reasoning about system dependability, thereby establishing a context for understanding the roles played by specific approaches presented in this book's two companion volumes. It then explores the range of models and analysis methods necessary to design, validate and analyze dependable systems. A companion to this book (published by Kluwer), subtitled Paradigms for Dependable Applications, presents a variety of specific approaches to achieving dependability at the application level. Driven by the higher level fault models of Models and Frameworks for Dependable Systems, and built on the lower level abstractions implemented in a third companion book subtitled System Implementation, these approaches demonstrate how dependability may be tuned to the requirements of an application, the fault environment, and the characteristics of the target platform. Three classes of paradigms are considered: protocol-based paradigms for distributed applications, algorithm-based paradigms for parallel applications, and approaches to exploiting application semantics in embedded real-time control systems. Another companion book (published by Kluwer) subtitled System Implementation, explores the system infrastructure needed to support the various paradigms of Paradigms for Dependable Applications. Approaches to implementing support mechanisms and to incorporating additional appropriate levels of fault detection and fault tolerance at the processor, network, and operating system level are presented. A primary concern at these levels is balancing cost and performance against coverage and overall dependability. As these chapters demonstrate, low overhead, practical solutions are attainable and not necessarily incompatible with performance considerations. The section on innovative compiler support, in particular, demonstrates how the benefits of application specificity may be obtained while reducing hardware cost and run-time overhead.


Book Synopsis Foundations of Dependable Computing by : Gary M. Koob

Download or read book Foundations of Dependable Computing written by Gary M. Koob and published by Springer Science & Business Media. This book was released on 2007-07-23 with total page 272 pages. Available in PDF, EPUB and Kindle. Book excerpt: Foundations of Dependable Computing: Models and Frameworks for Dependable Systems presents two comprehensive frameworks for reasoning about system dependability, thereby establishing a context for understanding the roles played by specific approaches presented in this book's two companion volumes. It then explores the range of models and analysis methods necessary to design, validate and analyze dependable systems. A companion to this book (published by Kluwer), subtitled Paradigms for Dependable Applications, presents a variety of specific approaches to achieving dependability at the application level. Driven by the higher level fault models of Models and Frameworks for Dependable Systems, and built on the lower level abstractions implemented in a third companion book subtitled System Implementation, these approaches demonstrate how dependability may be tuned to the requirements of an application, the fault environment, and the characteristics of the target platform. Three classes of paradigms are considered: protocol-based paradigms for distributed applications, algorithm-based paradigms for parallel applications, and approaches to exploiting application semantics in embedded real-time control systems. Another companion book (published by Kluwer) subtitled System Implementation, explores the system infrastructure needed to support the various paradigms of Paradigms for Dependable Applications. Approaches to implementing support mechanisms and to incorporating additional appropriate levels of fault detection and fault tolerance at the processor, network, and operating system level are presented. A primary concern at these levels is balancing cost and performance against coverage and overall dependability. As these chapters demonstrate, low overhead, practical solutions are attainable and not necessarily incompatible with performance considerations. The section on innovative compiler support, in particular, demonstrates how the benefits of application specificity may be obtained while reducing hardware cost and run-time overhead.

Design of Dependable Computing Systems

Design of Dependable Computing Systems

Author: J.C. Geffroy

Publisher: Springer Science & Business Media

Published: 2013-03-09

Total Pages: 678

ISBN-13: 9401598843

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This book analyzes the causes of failures in computing systems, their consequences, as weIl as the existing solutions to manage them. The domain is tackled in a progressive and educational manner with two objectives: 1. The mastering of the basics of dependability domain at system level, that is to say independently ofthe technology used (hardware or software) and of the domain of application. 2. The understanding of the fundamental techniques available to prevent, to remove, to tolerate, and to forecast faults in hardware and software technologies. The first objective leads to the presentation of the general problem, the fault models and degradation mechanisms wh ich are at the origin of the failures, and finally the methods and techniques which permit the faults to be prevented, removed or tolerated. This study concerns logical systems in general, independently of the hardware and software technologies put in place. This knowledge is indispensable for two reasons: • A large part of a product' s development is independent of the technological means (expression of requirements, specification and most of the design stage). Very often, the development team does not possess this basic knowledge; hence, the dependability requirements are considered uniquely during the technological implementation. Such an approach is expensive and inefficient. Indeed, the removal of a preliminary design fault can be very difficult (if possible) if this fault is detected during the product's final testing.


Book Synopsis Design of Dependable Computing Systems by : J.C. Geffroy

Download or read book Design of Dependable Computing Systems written by J.C. Geffroy and published by Springer Science & Business Media. This book was released on 2013-03-09 with total page 678 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book analyzes the causes of failures in computing systems, their consequences, as weIl as the existing solutions to manage them. The domain is tackled in a progressive and educational manner with two objectives: 1. The mastering of the basics of dependability domain at system level, that is to say independently ofthe technology used (hardware or software) and of the domain of application. 2. The understanding of the fundamental techniques available to prevent, to remove, to tolerate, and to forecast faults in hardware and software technologies. The first objective leads to the presentation of the general problem, the fault models and degradation mechanisms wh ich are at the origin of the failures, and finally the methods and techniques which permit the faults to be prevented, removed or tolerated. This study concerns logical systems in general, independently of the hardware and software technologies put in place. This knowledge is indispensable for two reasons: • A large part of a product' s development is independent of the technological means (expression of requirements, specification and most of the design stage). Very often, the development team does not possess this basic knowledge; hence, the dependability requirements are considered uniquely during the technological implementation. Such an approach is expensive and inefficient. Indeed, the removal of a preliminary design fault can be very difficult (if possible) if this fault is detected during the product's final testing.

Dependable Embedded Systems

Dependable Embedded Systems

Author: Jörg Henkel

Publisher: Springer Nature

Published: 2020-12-09

Total Pages: 606

ISBN-13: 303052017X

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This Open Access book introduces readers to many new techniques for enhancing and optimizing reliability in embedded systems, which have emerged particularly within the last five years. This book introduces the most prominent reliability concerns from today’s points of view and roughly recapitulates the progress in the community so far. Unlike other books that focus on a single abstraction level such circuit level or system level alone, the focus of this book is to deal with the different reliability challenges across different levels starting from the physical level all the way to the system level (cross-layer approaches). The book aims at demonstrating how new hardware/software co-design solution can be proposed to ef-fectively mitigate reliability degradation such as transistor aging, processor variation, temperature effects, soft errors, etc. Provides readers with latest insights into novel, cross-layer methods and models with respect to dependability of embedded systems; Describes cross-layer approaches that can leverage reliability through techniques that are pro-actively designed with respect to techniques at other layers; Explains run-time adaptation and concepts/means of self-organization, in order to achieve error resiliency in complex, future many core systems.


Book Synopsis Dependable Embedded Systems by : Jörg Henkel

Download or read book Dependable Embedded Systems written by Jörg Henkel and published by Springer Nature. This book was released on 2020-12-09 with total page 606 pages. Available in PDF, EPUB and Kindle. Book excerpt: This Open Access book introduces readers to many new techniques for enhancing and optimizing reliability in embedded systems, which have emerged particularly within the last five years. This book introduces the most prominent reliability concerns from today’s points of view and roughly recapitulates the progress in the community so far. Unlike other books that focus on a single abstraction level such circuit level or system level alone, the focus of this book is to deal with the different reliability challenges across different levels starting from the physical level all the way to the system level (cross-layer approaches). The book aims at demonstrating how new hardware/software co-design solution can be proposed to ef-fectively mitigate reliability degradation such as transistor aging, processor variation, temperature effects, soft errors, etc. Provides readers with latest insights into novel, cross-layer methods and models with respect to dependability of embedded systems; Describes cross-layer approaches that can leverage reliability through techniques that are pro-actively designed with respect to techniques at other layers; Explains run-time adaptation and concepts/means of self-organization, in order to achieve error resiliency in complex, future many core systems.

Dependability Benchmarking for Computer Systems

Dependability Benchmarking for Computer Systems

Author: Karama Kanoun

Publisher: John Wiley & Sons

Published: 2008-10-03

Total Pages: 384

ISBN-13: 0470370831

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A comprehensive collection of benchmarks for measuring dependability in hardware-software systems As computer systems have become more complex and mission-critical, it is imperative for systems engineers and researchers to have metrics for a system's dependability, reliability, availability, and serviceability. Dependability benchmarks are useful for guiding development efforts for system providers, acquisition choices of system purchasers, and evaluations of new concepts by researchers in academia and industry. This book gathers together all dependability benchmarks developed to date by industry and academia and explains the various principles and concepts of dependability benchmarking. It collects the expert knowledge of DBench, a research project funded by the European Union, and the IFIP Special Interest Group on Dependability Benchmarking, to shed light on this important area. It also provides a large panorama of examples and recommendations for defining dependability benchmarks. Dependability Benchmarking for Computer Systems includes contributions from a credible mix of industrial and academic sources: IBM, Intel, Microsoft, Sun Microsystems, Critical Software, Carnegie Mellon University, LAAS-CNRS, Technical University of Valencia, University of Coimbra, and University of Illinois. It is an invaluable resource for engineers, researchers, system vendors, system purchasers, computer industry consultants, and system integrators.


Book Synopsis Dependability Benchmarking for Computer Systems by : Karama Kanoun

Download or read book Dependability Benchmarking for Computer Systems written by Karama Kanoun and published by John Wiley & Sons. This book was released on 2008-10-03 with total page 384 pages. Available in PDF, EPUB and Kindle. Book excerpt: A comprehensive collection of benchmarks for measuring dependability in hardware-software systems As computer systems have become more complex and mission-critical, it is imperative for systems engineers and researchers to have metrics for a system's dependability, reliability, availability, and serviceability. Dependability benchmarks are useful for guiding development efforts for system providers, acquisition choices of system purchasers, and evaluations of new concepts by researchers in academia and industry. This book gathers together all dependability benchmarks developed to date by industry and academia and explains the various principles and concepts of dependability benchmarking. It collects the expert knowledge of DBench, a research project funded by the European Union, and the IFIP Special Interest Group on Dependability Benchmarking, to shed light on this important area. It also provides a large panorama of examples and recommendations for defining dependability benchmarks. Dependability Benchmarking for Computer Systems includes contributions from a credible mix of industrial and academic sources: IBM, Intel, Microsoft, Sun Microsystems, Critical Software, Carnegie Mellon University, LAAS-CNRS, Technical University of Valencia, University of Coimbra, and University of Illinois. It is an invaluable resource for engineers, researchers, system vendors, system purchasers, computer industry consultants, and system integrators.

Reliable Computer Systems

Reliable Computer Systems

Author: Daniel Siewiorek

Publisher: Digital Press

Published: 2014-06-28

Total Pages: 929

ISBN-13: 1483297438

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Enhance your hardware/software reliability Enhancement of system reliability has been a major concern of computer users and designers ¦ and this major revision of the 1982 classic meets users' continuing need for practical information on this pressing topic. Included are case studies of reliable systems from manufacturers such as Tandem, Stratus, IBM, and Digital, as well as coverage of special systems such as the Galileo Orbiter fault protection system and AT&T telephone switching processors.


Book Synopsis Reliable Computer Systems by : Daniel Siewiorek

Download or read book Reliable Computer Systems written by Daniel Siewiorek and published by Digital Press. This book was released on 2014-06-28 with total page 929 pages. Available in PDF, EPUB and Kindle. Book excerpt: Enhance your hardware/software reliability Enhancement of system reliability has been a major concern of computer users and designers ¦ and this major revision of the 1982 classic meets users' continuing need for practical information on this pressing topic. Included are case studies of reliable systems from manufacturers such as Tandem, Stratus, IBM, and Digital, as well as coverage of special systems such as the Galileo Orbiter fault protection system and AT&T telephone switching processors.

The Intellectual Foundation of Information Organization

The Intellectual Foundation of Information Organization

Author: Elaine Svenonius

Publisher: MIT Press

Published: 2000

Total Pages: 282

ISBN-13: 9780262194334

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Integrating the disparate disciplines of descriptive cataloging, subject cataloging, indexing, and classification, the book adopts a conceptual framework that views the process of organizing information as the use of a special language of description called a bibliographic language.


Book Synopsis The Intellectual Foundation of Information Organization by : Elaine Svenonius

Download or read book The Intellectual Foundation of Information Organization written by Elaine Svenonius and published by MIT Press. This book was released on 2000 with total page 282 pages. Available in PDF, EPUB and Kindle. Book excerpt: Integrating the disparate disciplines of descriptive cataloging, subject cataloging, indexing, and classification, the book adopts a conceptual framework that views the process of organizing information as the use of a special language of description called a bibliographic language.

Delta-4: A Generic Architecture for Dependable Distributed Computing

Delta-4: A Generic Architecture for Dependable Distributed Computing

Author: David Powell

Publisher: Springer Science & Business Media

Published: 2012-12-06

Total Pages: 477

ISBN-13: 3642846963

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Delta-4 is a 5-nation, 13-partner project that has been investigating the achievement of dependability in open distributed systems, including real-time systems. This book describes the design and validation of the distributed fault-tolerant architecture developed within this project. The key features of the Delta-4 architecture are: (a) a distributed object-oriented application support environment; (b) built-in support for user-transparent fault tolerance; (c) use of multicast or group communication protocols; and (d) use of standard off the-shelf processors and standard local area network technology with minimum specialized hardware. The book is organized as follows: The first 3 chapters give an overview of the architecture's objectives and of the architecture itself, and compare the proposed solutions with other approaches. Chapters 4 to 12 give a more detailed insight into the Delta-4 architectural concepts. Chapters 4 and 5 are devoted to providing a firm set of general concepts and terminology regarding dependable and real-time computing. Chapter 6 is centred on fault-tolerance techniques based on distribution. The description of the architecture itself commences with a description of the Delta-4 application support environment (Deltase) in chapter 7. Two variants of the architecture - the Delta-4 Open System Architecture (OSA) and the Delta-4 Extra Performance Architecture (XPA) - are described respectively in chapters 8 and 9. Both variants of the architecture have a common underlying basis for dependable multicasting, i. e.


Book Synopsis Delta-4: A Generic Architecture for Dependable Distributed Computing by : David Powell

Download or read book Delta-4: A Generic Architecture for Dependable Distributed Computing written by David Powell and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 477 pages. Available in PDF, EPUB and Kindle. Book excerpt: Delta-4 is a 5-nation, 13-partner project that has been investigating the achievement of dependability in open distributed systems, including real-time systems. This book describes the design and validation of the distributed fault-tolerant architecture developed within this project. The key features of the Delta-4 architecture are: (a) a distributed object-oriented application support environment; (b) built-in support for user-transparent fault tolerance; (c) use of multicast or group communication protocols; and (d) use of standard off the-shelf processors and standard local area network technology with minimum specialized hardware. The book is organized as follows: The first 3 chapters give an overview of the architecture's objectives and of the architecture itself, and compare the proposed solutions with other approaches. Chapters 4 to 12 give a more detailed insight into the Delta-4 architectural concepts. Chapters 4 and 5 are devoted to providing a firm set of general concepts and terminology regarding dependable and real-time computing. Chapter 6 is centred on fault-tolerance techniques based on distribution. The description of the architecture itself commences with a description of the Delta-4 application support environment (Deltase) in chapter 7. Two variants of the architecture - the Delta-4 Open System Architecture (OSA) and the Delta-4 Extra Performance Architecture (XPA) - are described respectively in chapters 8 and 9. Both variants of the architecture have a common underlying basis for dependable multicasting, i. e.