A dissertation submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in fulfilment Of the requirements for the degree of Master of Science in Engineering. Johannesburg, 1993 / Renewal is the extraction of the intellectual content (algorithms, data structures) from an existing program, and then puilding a new more maiatainable program using more modem progra1Tlming methods and languages. A survey of software structure on maintenance. highlighted the different hierarchies produced by functional and object-oriented design methods. Elecsim, a linear circuit sL~ulator written in Pascal, was chosen as the existing program to be renewed, The new version follows the approach of decoupling the user interface and introducing an explicit scheduler. The object-oriented design technique is used extensively. Other issues addressed include online-help and. documentation for the program. Conclusions are drawn which are generally applicable from the specificlessons learnt from the Elecsim/Elector case study. / MT2017