  We describe a scalable parallelization of Geant4 using commodity hardware in
a collaborative effort between the College of Computer Science and the
Department of Physics at Northeastern University. The system consists of a
Beowulf cluster of 32 Pentium II processors with 128 MBytes of memory each,
connected via ATM and fast Ethernet. The bulk of the parallelization is done
using TOP-C (Task Oriented Parallel C), software widely used in the
computational algebra community. TOP-C provides a flexible and powerful
framework for parallel algorithm development, is easy to learn, and is
available at no cost. Its task oriented nature allows one to parallelize legacy
code while hiding the details of interprocess communications. Applications
include fast interactive simulation of computationally intensive processes such
as electromagnetic showers. General results motivate wider applications of
TOP-C to other simulation problems as well as to pattern recognition in high
energy physics.
