The PHENIX online computing system

The Online Computing System (ONCS) is responsible for the overall configuration and control of the PHENIX detector system. The experiment is made up of 4 spectrometer arms with a total number of 11 subdetectors, which need to be operated by a single control and monitoring system. This includes the configuration of the individual components of the readout system, as well as the control of the state of the detector's data flow. Furthermore, the ONCS system sets up the environment for the online monitoring of the detectors. The slow control of high voltages and other ancillary devices is also part of the system. The ONCS system is designed around a distributed computing model which relies on CORBA object oriented technology, the ROOT system as the backbone of the online monitoring, and EPICS for the control of the High Voltage systems. Issues regarding the use and implementation of these technologies in the ONCS system are discussed, as well as the methods used to control the state and health of the PHENIX detector.