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From the earliest days of computers until the early 1970s, the trend in computer architecture was toward increasing complexity. This complexity revealed itself through the introduction of new instructions that matched the application areas. Microcode was an implementation technique that greatly facilitated this trend; thus, most computers were implemented using microcode. In 1975, work began at the Thomas J. Watson Research Center on an experimental minicomputer. This project, termed the 801 project, questioned the trend toward complexity in computer architecture. It was observed that most of the complex instructions were seldom used. Thus, a computer could be designed with only simple instructions without drastically increasing the path length or number of instructions required to implement an application. This made it possible to implement a machine without resorting to microcode, which improved performance. This paper described the background and evolution of these ideas in the context of the 801 experimental minicomputer project.
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