ABSTRACT
This chapter addresses the definition of software reliability, how software can be unreliable, why software reliability is important today, and the cost of unreliable software. There are many types of errors that will cause software to become unreliable. The ones just listed are some of the most common ones. Software can be unreliable when it does not perform the function that the end user intended or required. The cost of correcting a software error generally increases by magnitudes for every phase of the life cycle. Ideally, the errors found during the integration phase are those due to interfaces that could not have been easily or possibly found during previous phases. Ideally the number of errors detected levels off by the acceptance test phase. The cost benefit of detecting and correcting errors early in the life cycle can be shown by multiplying the number of errors found in each phase of the life cycle by the appropriate magnitude.
