The author's research of topologies of parallel computing systems and the tasks solved with them, including the corresponding tools of their modeling, is summarized in the present paper. The original topological model of such systems is presented based on the modified Amdahl law. It allowed formalizing the dependence of the necessary number of processors and the maximal distance between information-adjacent vertices in a graph on the directive values of acceleration or efficiency. The dependences of these values on the system interconnection topology and on the information graph of the parallel task are also formalized. The tools for a comparative evaluation of these dependences, topological criteria and the functions of scaling and fault-tolerant operation of parallel systems are based on the author|s technique of projective description of graphs and the algorithms used in it.