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Brooks particularly had in mind IBM's System 360. One of its goals was to have a single architecture span an extremely wide range of performance. So there were many models (e.g., 360-20, 360-65, 360-90) with a couple of orders of magnitude differences in cost and performance, but sharing a single architecture. Implementation teams built each model with attention to its specific required performance and cost constraints, leading to many different hardware designs. The system architects worked to define an architecture without constraining the possible implementations unnecessarily.