Operation and Performance of the CMS Level-1 Trigger during 7 TeV Collisions

The Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider (LHC) has been collecting data at center-of-mass energy 7 TeV since March 2010. CMS detects the products of proton beams colliding at a rate of 40 MHz. The Level-1 trigger reduces this collision rate to an output rate of 100 kHz, which is forwarded to the High-Level trigger, a dedicated computer farm, which reduces that further to a rate of 100 Hz, suitable for storage of full event data. The Level-1 trigger uses high-speed custom electronics to combine information from electromagnetic and hadronic calorimeters and three muon detection systems and identifies potential physics objects of interest in only a few microseconds. To ensure good performance of the Level-1 trigger hardware, robust configuration and monitoring software is also required. This talk will concentrate on the performance of the Level-1 trigger in the 2010 and ongoing 2011 collision runs, as well as presenting an overall picture of the hardware and operation.