The DAQ of the COMPASS experiment

COMPASS is a fixed target experiment at CERN's SPS. In 2002, a first physics run was completed with 260 TB of data recorded, corresponding to 5 billion events. The data acquisition architecture is based on custom frontends, buffers based on PCI cards, and server PCs networked via Gigabit Ethernet. A custom timing and trigger distribution system provides unique event identification and time synchronization. Results on the performance of the system and an outlook to improvements using online filtering will be given.