It is deemed substantial that understanding the conceptual differences between the hard-sphere Discrete Particle Model (DPM) and the event-driven Molecular Dynamics (MD) regarding the collision-event handling will help the design of new algorithms to increase the efficiency of collision-handling operations for DPM. The latter has gone largely unrecognized by most of the DPM-based numerical works on fluidization systems. We elaborated these differences and conceptually compared the only two O(1) time complexity algorithms developed for MD and DPM. It was shown that the hash-table strategy that takes into account the main features of fluidization systems increased considerably the efficiency of collision-handling algorithm for DPM. (C) 2009 Elsevier B.V. All rights reserved.