Tuning the Pentium Pro microarchitecture

Designing a wholly new microprocessor is difficult and expensive. To justify this effort, a major new microarchitecture must improve performance one and a half or two times over the previous-generation microarchitecture, when evaluated on equivalent process technology. In addition, semiconductor process technology continues to evolve while the processor design is in progress. The previous-generation microarchitecture increases in clock speed and performance due to compactions and conversion to newer technology. A new microarchitecture must "intercept" the process technology to achieve a compounding of process and microarchitectural speedups. This paper looks at a large microprocessor development project which reveals some of the reasoning (for goals, changes, trade-offs, and performance simulation) that lay behind its final form.