"CERN is a leading partner of the Worldwide LHC Computing Grid (WLCG) that provides the distributed computing infrastructure for scientists working on the LHC experiments. This infrastructure links more than 300 computer centers and provides access to 260,000 CPUs on which users run about 20 million jobs every month. These machines are operated under several GNU/Linux variants.
At CERN roughly 10,000 systems run different distributions of GNU/Linux. These machines are part of central services, experiment-specific systems and end user desktops.
The middleware stacks that federate the distributed resources in a computing grid are free software too. The most prevalent being gLite (about 1.2 million lines of code). Almost all packages used by physicists to simulate and analyze their data, like ROOT and GEANT4, are also available under free software licenses.
It is no exaggeration to say that for most scientists, the open and free software model has always been the most natural one.
CERN is one of the main hubs of the High Energy Physics community. Computing has been one of the essential tools of this research field since it started and code has been shared for more than 40 years. For some areas of our research, the software used has an impact on the published results and as a consequence always has to be open to the scrutiny of other researchers. It is no exaggeration to say that for most scientists, the open and free software model has always been the most natural one. Cooperation across borders and institutions has always been essential for our highly distributed community and free software simplifies this immensely.
The use and adaptation of free software outside the core of scientific work became more important for CERN with the increased use of UNIX-like systems, especially as the development of our grid middleware would have been impossible without the use of free software."