  In October and November 2008, the CMS collaboration conducted a programme of
cosmic ray data taking, which has recorded about 270 million events. The
Resistive Plate Chamber system, which is part of the CMS muon detection system,
was successfully operated in the full barrel. More than 98% of the channels
were operational during the exercise with typical detection efficiency of 90%.
In this paper, the performance of the detector during these dedicated runs is
reported.
