ATLAS data acquisition

ATLAS is a general purpose high energy physics experiment at the Large Hadron Collider. The trigger and data acquisition (DAQ) system is designed to handle the extremely high data rates. The three level ATLAS trigger system (Level 1, Level 2 and Event Filter) reduces the data rate from 40 MHz bunch crossing down to ~200 Hz. The DAQ system is designed to transport data at different trigger levels to the mass storage, with main subsystems including the dataflow, a combination of custom designed components and commodity processors running multithread software applications and connected by Gigabit Ethernet, the online software responsible for the configuration, control and information sharing of the system, and the monitoring software responsible for the data quality assurance. The system is being continuously commissioned in situ with detectors, to take cosmic data and the LHC beam data in 2008.