An overview of the STAR DAQ system

We describe the STAR Data Acquisition System. STAR is one of four experiments commissioned at the Relativistic Heavy Ion Collider (RHIC) at BNL in 1999 and 2000. DAQ combines custom VME-based receiver electronics with off-the-shelf computers in a parallel architecture interconnected with a Myrinet network. Events of size 80 MB are processed at input rates up to 100 Hz. Events are reduced to 10 MB by zero suppression performed in hardware using custom-designed ASICs. A Level 3 Trigger reconstructs tracks in real time and provides a physics-based filter to further reduce the sustained output data rate to ∼30 MB/s. Built events are sent via Gigabit Ethernet to the RHIC Computing Facility and stored to tape using HPSS.