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