This paper presents the similarities and differences between hardware, software and system reliability. Relative contributions to system failures are shown for software and hardware and failure and recovery propensities are also discussed. Reliability, availability and maintainability (RAM) concepts have been broadly developed for software reliability than hardware reliability. Extending these software concepts to hardware and system reliability helps in examining the reliability of complex systems.The paper concludes with assurance techniques for defending against faults. Most of the techniques discussed originate in software reliability but apply to all aspects of a system. Also, the effects of redundancy on overall system availability are shown.
& Conclusions-This paper reviews the progress in software reliability over the past 15 years and discusses the best tools and practices that can be applied today. Software is seen to play an increasingly vital role over time, vis-avis hardware, in terms of system content. The software content is increasing and, often today, it is a key factor in safety critical applications in medicine, transportation, and nuclear energy. Significant software content is found in almost every system, appliance, and machine which we use. In addition, software is the backbone of our business enterprise operations. Consequently, producing reliable software is a mandate. Its development is often the "long pole in the tent" driving the cycle time required to produce and field a product. Most often, software is the main source of system reliability problems. The best development practices are recommended, herein, for managing the reliability of software. The development of software reliability models and userfriendly tool kits is described. These tools allow software reliability to be measured, tracked, and improved to meet the customer's specified reliability. The ability to measure software reliability promotes development focus, and consequently, its improvement.
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