  The Run Control and Monitor System (RCMS) of the CMS experiment is the set of
hardware and software components responsible for controlling and monitoring the
experiment during data-taking. It provides users with a "virtual counting
room", enabling them to operate the experiment and to monitor detector status
and data quality from any point in the world. This paper describes the
architecture of the RCMS with particular emphasis on its scalability through a
distributed collection of nodes arranged in a tree-based hierarchy. The current
implementation of the architecture in a prototype RCMS used in test beam
setups, detector validations and DAQ demonstrators is documented. A discussion
of the key technologies used, including Web Services, and the results of tests
performed with a 128-node system are presented.
