The Event Builder and Level 3 trigger systems of the CDF experiment at Ferm
ilab are required to process about 300 events per second, with an average e
vent size of similar to 200 KB. In the event building process the event is
assembled from 15 sources supplying event fragments with roughly equal size
s 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 h
as been chosen. It is based on commodity components: VME-based CPU's for th
e data read out, an ATM switch for the event building and Pentium-based per
sonal computers running the Linux operating system for the event processing
. Event flow through ATM is controlled by a reflective memory ring. The rou
ghly homogeneous distribution of the expected load allows the use of 100 Mb
ps 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.