LCG: A worldwide computer grid for physics

Several new experiments in particle physics are being prepared by large international consortia. During their lifetimes they will generate an unprecedented amount of petabytes (1015 B) of data, which have to be made accessible to large communities of researchers, distributed all over the world - this fact is one of the biggest challenges facing modern experimental physics. A possible solution is provided by the concept of a distributed computing Grid, made feasible by recent significant improvements in networking. Based on the results of several pilot Grid projects on both sides of the Atlantic, the LHC Computing Grid (LCG) project was launched in 2001, with the goal of creating a large prototype of a worldwide computing Grid for physics. Thousands of processors and a number of mass storage devices, belonging to different institutions of many countries, have been connected effectively into one computing system, controlled by the "virtual organizations" of experiments. This paper presents estimates of the computing requirements of future experiments, an overview of the Grid technology as well as progress on the construction of a computing Grid for particle physics and its use by the experiments.