With the rapid development and wideapplications of computing systems on which more reliance has been put, adependable system will be much more important than ever. This paper isfirst aimed at giving informal but precise definitions characterizingthe various attributes of dependability of computing systems and thenthe importance of (and the relationships among) all the attributes areexplained.Dependability is first introduced as a global concept which subsumes theusual attributes of reliability, availability, maintainability, safetyand security. The basic definitions given here are then commended andsupplemented by detailed material and additional explanations in thesubsequent sections.The presentation has been structured as follows so as to attract thereaders attention to the important attributions of dependability.* Search for a few number of concise concepts enabling thedependability attributes to be expressed as clearly as possible.* Use of terms which are identical or as close as possible tothose commonly used nowadays.This paper is also intended to provoke peoples interest in designing adependable computing system.