The NA48 on-line PC farm

The NA48 experiment at the CERN SPS measures the direct CP violation parameter $\Re(\epsilon'/\epsilon)$ in the neutral kaon system with an intended precision of $ 2 \times 10^{-4}$. Thus, the data acquisition system has to handle peak rates up to 150 MByte/s during a 2.5 s beam burst and flat rates up to 20 MByte/s during on-line processing. The NA48 on-line PC farm includes 24 PentiumII-266 MHz PCs connected via switched fast ethernet network. This farm receives data from the detector systems and performs event building. Afterwards the data are transferred via an optical gigabit ethernet link to the NA48 central data recording system at CERN computer center. In addition, trigger and checking processes can be applied. The software on the farm is implemented as client/server applications and represents a highly flexible, fail safe, and scalable system. During data taking, in 1999, 100 TByte were collected, processed, and stored by the acquisition system with an overall efficiency of 99%.