A. Wagner (CERN)
CERN has about 5500 Desktop PCs. These computers offer a large pool of resources that can be used for physics calculations outside office hours. The paper describes a project to make use of the spare CPU cycles of these PCs for LHC tracking studies. The client server application is implemented as a lightweight, modular screensaver and a Web Application containing the physics job repository. The information exchange between client and server is done using the HTTP protocol. The design and implementation is presented together with results of performance and scalability studies. A typical LHC tracking study involves some 1500 jobs, each over 100,000 turns, requiring about 1 hour of CPU on a modern PC. A reliable and easy to use Linux interface to the CPSS Web application has been provided. It has been used for a production run of 15,000 jobs, using some 50 desktop Windows PCs, which uncovered a numerical incompatibility between Windows 2000 and XP. It is expected to make available up to two orders of magnitude more computing power for these studies at zero cost.