Requirements, Bottlenecks, and Good Fortune: Agents for Microprocessor Evolution

operated at a clock frequency of 108 kHz. Today, 30 years later, the microprocessor contains almost 200 million transistors, operating at a frequency of more than 1 GHz. In five years, those numbers are expected to grow to more than a billion transistors on a single chip, operating at a clock frequency of from 6 to 10 GHz. The evolution of the microprocessor, from where it started in 1971 to where it is today and where it is likely to be in five years, has come about because of several contributing forces. Our position is that this evolution did not just happen, that each step forward came as a result of one of three things, and always within the context of a computer architect making tradeoffs. The three things are: 1) new requirements; 2) bottlenecks; and 3) good fortune. I call them collectively agents for evolution. This article attempts to do three things: describe a basic frame-work for the field of microprocessors, show some of the important developments that have come along in the 30 years since the ar-rival of the first microprocessor, and finally, suggest some of the new things you can expect to see in a high-performance micropro-cessor in the next five years. Keywords—Computer architecture, microarchitecture, micro-processor, microprocessor design, microprocessor evolution. I. BASIC FRAMEWORK A. Computer Architecture: A Science of Tradeoffs Computer architecture is far more “art ” than “science.” Our capabilities and insights improve as we experience more cases. Computer architects draw on their experience with previous designs in making decisions on current projects. If computer architecture is a science at all, it is a science of tradeoffs. Computer architects over the past half century have continued to develop a foundation of knowledge to help them practice their craft. Almost always the job of the computer ar-chitect requires using that fundamental knowledge to mak