ATLAS silicon microstrip tracker operation and performance

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In December 2009 the ATLAS experiment at the CERN Large Hadron Collider (LHC) recorded the first proton-proton collisions at a center-of-mass energy of 900 GeV and this was followed by the unprecedented energy of 7 TeV in March 2010. The SemiConductor Tracker (SCT) is the key precision tracking device in ATLAS, made up from silicon microstrip detectors processed in the planar p-in-n technology. The completed SCT has been installed inside the ATLAS experimental hall. After the commissioning phase it arrived to the first LHC pp collision runs in very good shape: 99.3% of the SCT modules are operational, noise occupancy and hit efficiency exceed the design specifications, the alignment is already close enough to the ideal one to allow on-line track reconstruction and invariant mass determination. This overview presents the current status of the SCT, including results from the latest data-taking periods in 2009 and 2010, and from the detector alignment. We report on the operation of the detector and observed problems. The main emphasis is given to the performance of the SCT with the LHC in collision mode in a comparison with the expected parameters and with the Monte-Carlo simulations.