3.2.3 Each replaceable part should be simple to replace and should be constructed for easy and safe handling. All replaceable parts should be so arranged that it is not possible to connect them incorrectly or to use incorrect replacements. Where this is not practicable, the replaceable parts, including their means of electrical connection, should be clearly marked.
3.3 Software
3.3.1 Systematic procedures should be followed during all phases of the software life cycle (development, installation and subsequent modification).
3.3.2 System tests should be specified, performed and documented. These tests should include all software functions and important combinations of functions, performance, dependability and usability requirements under all modes of operation including emergency conditions and behaviour under failure conditions.
3.3.3 Modifications of program contents and data, as well as a change of version, should be documented.
Note： ISO 9000-3 Gives guidelines for the application of ISO 9001 to the development, supply and maintenance of software.
4 System Configuration
4.1 General
4.1.1 The hardware and software should be of a modular, hierarchical, design in order to maximise the fault tolerance of the system.
4.1.2 The selection of the computer equipment should be consistent with safe operation of the system under control.
4.2 Self-test
4.2.1 Computer-based systems should be monitored for correct operation and an alarm should be given for an abnormal condition.
4.3 Power supply
4.3.1 The power supply should be monitored for failure and should give an alarm in the event of an abnormal condition.
4.3.2 Program and data held in the system should be protected from corruption by loss of power.
4.3.3 Redundant systems should be selectively fed and separately protected against short circuits and overloads.
