This standard is applicable to highly reliable software required for computers to be used for safety functions - class 1 functions according to IEC Publication 643. This includes the safety actuation systems, the safety system support features and the protection system. It is important to note that this standard establishes no additional fuctional requirements for safety systems. It discusses the software system principles and requirements and should be read in association with appropriate standards on computer hardware and system integration. Annexes A to F include considerations and tables on system development life cycle and details of software requirements, detailed recommendations for the development (design and coding) of safety related software, an outline for the software performance specification, language, translator, linkage editor, etc., software testing, and a list of*documents needed.