Engineering a Large Application Software Project: The Controls of the CERN PS Accelerator Complex

The CERN PS accelerator complex has been progressively converted to tull computer controls without interrupting its tull-time operation (more than 6000 hours per year with on average not more than 1% of the total down-time due to controls). The application software amounts to 120 man-years and 450´000 instructions; it compares with other large software projects, also outside the accelerator world: e.g. Skylab´s ground support software.1 This paper outlines the application software structure which takes into account technical requirements and constraitnts (resulting from the complexity of the process and its operation) and economical and managerial ones. It presents the engineering and management techniques used to promote implementation, testing and commissioning within budget, manpower and time constraints and concludes with experience gained.