Event Builder and Level 3 trigger at the CDF experiment

The Event Builder and Level 3 trigger systems of the CDF experiment at Fermilab are required to process about 300 events per second, with an average event size of similar to 200 KB. In the event building process the event is assembled from 15 sources supplying event fragments with roughly equal sizes of 12-16 KB. In the subsequent commercial processor-based Level 3 trigger, the events are reconstructed and trigger algorithms are applied. The CPU power required for filtering such a high data throughput rate exceeds 45000 MIPS. To meet these requirements a distributed and scalable architecture has been chosen. It is based on commodity components: VME-based CPU's for the data read out, an ATM switch for the event building and Pentium-based personal computers running the Linux operating system for the event processing. Event flow through ATM is controlled by a reflective memory ring. The roughly homogeneous distribution of the expected load allows the use of 100 Mbps Ethernet for event distribution and collection within the Level 3 system. Preliminary results from a test system obtained during the last year are presented. (C) 2001 Elsevier Science B.V. All rights reserved.