The trigger of ZEUS, a flexible system for a high bunch crossing rate collider

The trigger of the ZEUS experiment at HERA is based on a dead-time free, pipelined first level processor, a transputer network second level and a traditional computer farm at the third level. The environment at HERA, with a fast (96 ns) bunch crossing repetition rate and a high hadronic background, anticipates much more extreme conditions than the LHC experiments will face. We describe the design strategies and the results of ZEUS, with emphasis on the flexibility of the system that allowed us to satisfy the physics requirements that changed with increasing luminosity.