Event builder and level 3 at the CDF experiment

The Event Builder and Level 3 systems constitute critical components of the DAQ in the Collider Detector at Fermilab experiment. These systems are responsible for collecting data fragments from the Front End electronics, assembling the data into complete event records, reconstructing the events and forming the final trigger decision. With Tevatron Run IIa in progress, the systems have been running successfully at high throughput rates, the design utilizing scalable architecture and distributed event processing to meet the requirements. Brief descriptions of current performance in Run IIa and possible upgrade for Run IIb are presented. (C) 2003 Elsevier B.V. All rights reserved.