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A parallel computer for high-speed execution of expert system programs has been designed and implemented at the Oak Ridge National Laboratory. Programs written in the popular OPS5 language for serial machines need not be modified by the programmer, since the compiler on this special-purpose machine automatically employs the parallelism inherent in the language. Tasks are automatically distributed to parallel rule processors which can evaluate OPS5 rules in parallel. Performance improvements of a factor of 10 over serial machines have already been demonstrated. Enhancements are under way to attain a performance improvement of 100 or more over serial machines for artificial intelligence applications requiring the evaluation of thousands of rules each recognize-act cycle. The initial hardware implementation of the parallel architecture consists of a host computer that broadcasts to 64 parallel rule processors over a transmit-only bus. The communication time is kept to a minimum by using direct-memory access and a memory-mapped addressing scheme that permit each of the parallel rule processors to receive the appropriate information simultaneously. A wired-OR completion flag signals the host whenever all of the parallel rule processors have finished their recognition tasks. The host then extracts information from those rule processors whose rules have been satisfied and, based on a global criterion, selects one of these rules. The host then carries out the actions dictated by this rule and broadcasts new information to the rule processors to begin another recognize-act cycle. Statistics detailing the activities of the host and all of the rule processors are collected and displayed in real time. Thus, the performance of the various aspects of the architecture can be readily analyzed. Also, the execution of the expert system program itself can be studied to detect situations that may be altered to permit additional speedup.
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