Thirty Years of Collaboration with Jan van Leeuwen: In Search of Understanding Computation

I have collaborated with Jan van Leeuwen since the beginning of the 1980s. The non-standard models of computations have been the central subject of our joint work. Among these models, we focused especially onto realistic models of supercomputers, interactive computing, hypercomputing, characterization of contemporary computing in terms of extended Turing machine paradigm, and viewing computations as unbounded processes. This note describes the main models designed and investigated during this period, summarizes the most important results and gives references to the respective papers.