This standard specifies and classifies measures of the software aspects of dependability. It is an expansion of the scope of the existing standard; the revision includes the following aspects of dependability: reliability@ availability@ and maintainability of software. The applicability of this standard is any software system; in particular@ it applies to mission critical systems@ where high reliability@ availability@ and maintainability are of utmost importance. These systems include@ but are not limited to@ systems for military combat@ space missions@ air traffic control@ network operations@ stock exchanges@ automatic teller machines@ and airline reservation systems.