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% The XtremWeb-CH environment
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+
+High performance computing environments like MPI (Message Passing
+Interface) \cite{Gro94} are widely used and have proved their efficiency. This
+class of systems are very tightly coupled and powerful but not very error
+tolerant. Cluster computing environments like Condor
+\cite{condor-practice} and volunteer computing systems like BOINC \cite{boinc} are loosely coupled and
+have a scheduler that distributes tasks to computing nodes. Cluster
+computing environments assume the fact that nodes are in general
+directly accessible, one to another, but this does not apply to
+volunteer computing systems.
+
XtremWeb-CH (XWCH) is a volunteer computing inspired large-scale
-computing platform for distributed applications. It consists in three
-components: one coordinator, a set of workers and at least one
+computing platform for distributed applications. In fact, it tends to
+be a good compromise between cluster computing and volunteer
+computing. It is originaly based on another platform called XtremWeb
+ \cite{xtremweb}. It is easy to install, maintain, and it is supported by a Grid
+middleware (ARC \cite{arc}) and a workflow engine (JOpera \cite{JOpera}). It consists in
+three components: one coordinator, a set of workers, and at least one
warehouse. Client programs use these components.
The coordinator is the main component of the XWCH platform. It
