Data reduction systems for HEP experiments

Fast logic triggers are described which are capable of rejecting unwanted events during HEP experiments. Classes of track patterns are defined by entries in read/write memories and can be readily changed. Readout information from multiwire chambers addresses these memories and their outputs are processed by fast combinational logic to produce trigger decisions. In the circumstances where speed of decision making is not the prime consideration a much cheaper serial-parallel decision sequence may be implemented which, although slower in operation, can offer a very good definition of the tracks generated in a given data intake. Triggers of both categories are currently being used in experiments mounted at DESY and at CERN.