This article presents the base-line design and implementation of the ATLAS Trigger and Data Acquisition system, in particular the Data Flow and High Level Trigger components. The status of the installation and commissioning of the system is also presented.

Abstract-In the ATLAS experiment at the LHC, the output of readout hardware specific to each subdetector will be transmitted to buffers, located on custom made PCI cards ("ROBINs"). The data consist of fragments of events accepted by the first-level trigger at a maximum rate of 100 kHz. Groups of four ROBINs will be hosted in about 150 Read-Out Subsystem (ROS) PCs. Event data are forwarded on request via Gigabit Ethernet links and switches to the second-level trigger or to the Event builder. In this paper a discussion of the functionality and real-time properties of the ROS is combined with a presentation of measurement and modelling results for a testbed with a size of about 20% of the final DAQ system. Experimental results on strategies for optimizing the system performance, such as utilization of different network architectures and network transfer protocols, are presented for the testbed, together with extrapolations to the full system.

Abstract-The. This paper reviews the experience gained in the test beam, describes the current status and discusses the further enhancements to be made. We address issues related to the dataflow, integration of selection algorithms, testing, software distribution, installation and improvements.

Abstract-The base-line design and implementation of the ATLAS DAQ DataFlow system is described. The main components of the DataFlow system, their interactions, bandwidths, and rates are discussed and performance measurements on a 10% scale prototype for the final ATLAS TDAQ DataFlow system are presented. This prototype is a combination of custom design components and of multithreaded software applications implemented in C++ and running in a Linux environment on commercially available PCs interconnected by a fully switched gigabit Ethernet network.