The Leibniz Supercomputing Centre (LRZ) and the Bavarian Competence Network for Technical and Scienti?c High Performance Computing (KONWIHR) publish in the present book results of numerical simulations facilitated by the High P- formance Computer System in Bavaria (HLRB II) within the last two years. The papers were presented at the Fourth Joint HLRB and KONWIHR Review and - sult Workshop in Garching on 8th and 9th December 2009, and were selected from all progress reports of projects that use the HLRB II. Similar to the workshop two years ago, the majority of the contributed papers belong to the area of computational ?uid dynamics (CFD), condensed matter physics, astrophysics, chemistry, computer sciences and high-energy physics. We note a considerable increase of the user c- munity in some areas: Compared to 2007, the number of papers increased from 6 to 12 in condensed matter physics and from 2 to 5 in high-energy physics. Bio s- ences contributed only one paper in 2007, but four papers in 2009. This indicates that the area of application of supercomputers is continuously growing and entering new ?elds of research. The year 2007 saw two major events of particular importance for the LRZ. First, after a substantial upgrade with dual-core processors the SGI Altix 4700 superc- puter reached a peak performance of more than 62 Tera?op/s. And second, the n- pro?t organization Gauss Centre for Supercomputing e. V. (GCS) was founded on April 13th.

For the fourth time, the Leibniz Supercomputing Centre (LRZ) and the Com- tence Network for Technical, Scienti c High Performance Computing in Bavaria (KONWIHR) publishes the results from scienti c projects conducted on the c- puter systems HLRB I and II (High Performance Computer in Bavaria). This book reports the research carried out on the HLRB systems within the last three years and compiles the proceedings of the Third Joint HLRB and KONWIHR Result and Reviewing Workshop (3rd and 4th December 2007) in Garching. In 2000, HLRB I was the rst system in Europe that was capable of performing more than one Tera op/s or one billion oating point operations per second. In 2006 it was replaced by HLRB II. After a substantial upgrade it now achieves a peak performance of more than 62 Tera op/s. To install and operate this powerful system, LRZ had to move to its new facilities in Garching. However, the situation regarding the need for more computation cycles has not changed much since 2000. The demand for higher performance is still present, a trend that is likely to continue for the foreseeable future. Other resources like memory and disk space are currently in suf cient abundance on this new system.