The basic principles for the design of systeme important to the safety of nuclear power stations have been defined in existing standards such as the IAES Safety Guides 50-SG-D3 and D8 with a view to hardwired systems. This standard interprets these principles for the utilization of digital systems hardware for systems important to safety. This includes multiprocessor distributed systems and large scale central processor systems constructed from off-the-shelf items or from newly developed hardware. It lays down requirements specific to the hardware of digital systems. For specific requirements for computer software and common areas of hardware and software IEC 880 is applicable. Requirements for redundancy, independence and structural distribution are given. This standard constitutes a supplements to the safety classes requirements.