Running the Second Level Trigger Software on a Large Commercial Cluster

This note describes the porting and the evaluation of theso-called Reference Software developed within the Second Level Triggercommunity of the ATLAS experiment on the Paderborn SCI Cluster (PSC),a large compute cluster installed at the Paderborn Center forParallel Computing (PC2). The PSC consists of 96 dual-CPU PCsinterconnected using the Scalable Coherent Interface (SCI).Communication is based on the Message Passing Interface (MPI). Extensive studies have been carried out in order to understandboth the intrinsic performance of the system and the performanceand scalability of the Reference Software.