The performance of the DAQ and online system of the PHENIX experiment in run 4

PHENIX is one of two large experiments at Brookhaven National Laboratory's Relativistic Heavy Ion Collider (RHIC). The PHENIX experiment had a very successful run 4 in early 2004. Compared to previous runs, we were able to almost quadruple the data rate and to collect more than 200TB of data for the Au-Au system. In addition, we now have a mature and reliable online monitoring system in place which allows to ensure a high quality of the data. We made significant progress toward the goal to determine all informations required for the subsequent reconstruction and analysis of the data, such as calibration constants, in a near-line fashion, which greatly expedites the offline analysis of the data. We will give a brief overview of the system, and cover the areas where we achieved significant improvements over the previous runs.