Most Prolog machines have been based on specialized architectures. The authors' goal is to start with a general-purpose architecture and determine a minimal set of extensions for high-performance Prolog execution. They have developed both the architecture and optimizing compiler simultaneously, drawing on results of previous implementations. They find that most Prolog-specific operations can be done satisfactorily in software; however, there is a crucial set of features that the architecture must support to achieve the best Prolog performance. The emphasis in this study is on the authors' architecture and instruction set. The costs and benefits of the special architectural features and instructions are analyzed. Simulated performance results are presented and indicate a peak compiled Prolog performance of 3.68 million logical inferences per second.<<ETX>>