Implementation of a PC-Based Event Filter

This document describes an implementation of a PC-based Event Filter for ATLAS. Included are discussions of both the treatment of the dataflow and the monitoring/supervision aspects of the software. The emphasis in this implementation is on simplicity. In the case of the dataflow an effort has been made to simplify the interface between the Event Filter control processes and the Processing Tasks. The implementation of the monitoring/supervision software has been simplified by exploiting the services of the Online Software system as far as possible. Direct comparisons are made with an alternative implementation of the Event Filter.