  The pixel detector of the Compact Muon Solenoid experiment consists of three
barrel layers and two disks for each endcap. The detector was installed in
summer 2008, commissioned with charge injections, and operated in the 3.8 T
magnetic field during cosmic ray data taking. This paper reports on the first
running experience and presents results on the pixel tracker performance, which
are found to be in line with the design specifications of this detector. The
transverse impact parameter resolution measured in a sample of high momentum
muons is 18 microns.
