Reliability improvement of large series-parallel systems

The following excess methods of improving reliability of two-state series-parallel systems are presented: hot reserve, cold reserve and mixed (hot and cold) reserve of single components. There is also introduced the method of system reliability improving by replacing their components by more reliable ones. New theorems on two-state limit reliability functions of homogeneous and non-homogeneous series-parallel large systems composed of components with improved reliability are presented and applied to comparison the effects of these systems different reliability improving methods.