Practical Reliability Engineering, 5th Edition

10

Software Reliability

10.1 Introduction

Software is now part of the operating system of a very wide range of products and systems, and this trend continues to accelerate with the opportunities presented by low cost microcontroller devices. Software is relatively inexpensive to develop, costs very little to copy, weighs nothing, and does not fail in the ways that hardware does. Software also enables greater functionality to be provided than would otherwise be feasible or economic. Performing functions with software leads to less complex, cheaper, lighter and more robust systems. Therefore software is used increasingly to perform functions that otherwise would be performed by hardware, and even by humans. Recent examples are aircraft flight control systems, robotic welders, engine control systems, domestic bread-making machines, and so on.

The software ‘technology’ used today is the same basic sequential digital logic first applied in the earliest computers. The only significant changes have been in the speed and word length capability of processors and the amount of memory available, which in turn have enabled the development of high-level computer languages and modern operating systems. Some attempts have been made to develop radically different approaches such as parallel processing and fuzzy logic, but these remain fringe applications. Therefore, the basic principles of software development, to ensure that programs are correct, safe and reliable, remain largely unchanged since ...