1.1 General This International Standard is applicable to NPP computer-system hardware for systems of Class 1 and 2 (as defined by IEC 61513). The structure of this standard has not changed significantly from the original 1989 issue; however, some issues are now covered by standards which have been issued in the interim (for example, IEC 61513 for system architecture design) and references to new standards have been provided where applicable. The text of the standard has also been modified to reflect developments in computer system hardware design, the use of pre-developed (for example, COTS) hardware and changes in terminology. Computer hardware facilities used for software loading and checking are not considered to form an intrinsic part of a system important to safety and, as such, are outside the scope of this standard. NOTE 1 Class 3 computer-system hardware is not addressed by this standard, and it is recommended that such systems should be developed to commercial grade standards. NOTE 2 In 2006 the development of a new standard to address hardware requirements for "very complex" hardware was discussed within IEC SC 45A. If such a standard is developed then that standard would be used for the development of "very complex" hardware in preference to IEC 60987.