The PERCS system was designed by IBM in response to a DARPA challenge that called for a high-productivity high-performance computing system. The IBM PERCS architecture is a two level direct network having low diameter and high bisection bandwidth. Mapping and routing strategies play an important role in the performance of applications on such a topology. In this paper, we study mapping strategies for PERCS architecture, that examine how to map tasks of a given job on to the physical processing nodes. We develop and present fundamental principles for designing good mapping strategies that minimize congestion. This is achieved via a theoretical study of some common communication patterns under both direct and indirect routing mechanisms supported by the architecture. © 2012 IEEE.