The Geant4-Based Simulation Software of the ATLAS Detector

The ATLAS detector is a general purpose experiment which will study frontier physics by observing the collisions of two proton beams. It is presently under construction at CERN's Large Hadron Collider. Its instrumentation will cover a volume of about 22800 m around the interaction point. The simulation software is foreseen to be in use for more than 15 years and it must be, during this long period of time, easily maintainable and extensible. The intrinsic complexity of the geometry calls for a high degree of configurability so to allow to perform the simulation of only one part of the detector, or with different configurations of the magnetic field. Moreover, being the simulation of full physical events a time consuming process, simulation jobs will be run using extensively Grid technologies. We will give a complete review of the status of the Geant4-based ATLAS simulation software, nowadays fully functional, with particular stress on configurability issues and performance measurements.