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2021-07-20 15:00:15

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At the recent ISCA, there was a panel session with some of the major contributors to microprocessor development during the last 50 years. They were also asked to predict how they thought the microprocessor would develop during the next 25 years, going out to 2045. Just as a reminder, the panel was:

It is probably going too far to say that there were any conclusions from a discussion like that, but a few common themes did emerge. I'll take a look at them and add some of my own color.

One quote from Shekhar is that there have been no significant architectural advances since the 1970s and the IBM 370. As it happens, that's a computer I'm very familiar with since Cambridge University ran its university-wide time-sharing service on an IBM 370/165. I heard similar sentiments at a Microprocessor Forum years ago when someone (I forget who) pointed out that all the architectural innovation up to that point (pipelining and caches, I don't think speculative execution was on the scene then) had resulted in a 6X speedup. All the rest of the hundreds or thousands of times speedup since whatever you took as your base year was due to Moore's Law.

Shekhar's point is slightly different: that all the architectural innovation in microprocessors was just taking innovation that already existed in mainframes and other non-microprocessor computers, and moving it into silicon. Dave Patterson's big insight about RISC was another wrinkle. He realized that if nothing changed, then microcode would be moved from mainframes into microprocessors, and that it would be a disaster since microcode always needed a way to update it and in a silicon context that was not really feasible. His conclusion: get rid of the microcode and just run the object code directly on the micro-engine.

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