The ATLAS Readout System for LHC Runs 2 and 3

Abstract The ReadOut System (ROS) is a central part of the data acquisition (DAQ) system ATLAS Experiment at CERN Large Hadron Collider (LHC). responsible for receiving and buffering event from all detector subsystems serving these to High Level Trigger (HLT) via 10 GbE network, discarding or transporting onward once trigger has completed its selection process. ROS was completely replaced during 2013–2014 experimental shutdown in order meet demanding conditions expected LHC Run 2 3 (2015–2025). consists roughly one hundred Linux-based 2U-high rack-mounted servers equipped with PCIe I/O cards interfaces. This paper documents requirements Runs design choices taken them. results performance measurements re-use technology development sources, test platforms other systems, another DAQ component, namely Region Interest Builder (RoIB), are also discussed. Finally operations presented before looking upgrade 3.