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Comment by pmarin | Hacker News Reader

My bittorrent machine is a P-III Coppermine at 667 Mhz. I found it in the middle of the street a year ago.

It's still a bit amazing to think back on that period, where you could get 50% gains in a year. I remember dropping a big chunk of my savings as a teenager to buy a 700 coppermine, 4 years later they were sitting on roads even if they still worked perfectly.

Clock speed was king then. I'm sure everyone remembers when they stalled out ramping up the clock speed around 3.4-3.6GHZ and then it's pretty much been "back to the drawing board" ever since.

Fun fact: The Pentium 4 was originally anticipated by Intel to eventually run at 10 GHz after a few years of process shrink. Seriously.

Fun fact: If Intel wanted to, they could release a 10 GHz Pentium 4 design CPU. But it would be single-core and draw 500W, and require a many-thousands-of-dollars cooling system.

Intel was quite correct in predicting that we would continue to get faster transistors, and the Pentium 4 was absolutely the right design to take advantage of faster transistors. The story of the past decade of CPU architecture is all about heat becoming a primary design problem for the first time in history.

The point is that they grossly underestimated the impact of the power wall. They were aware of the power issue and you can find early papers by Pentium 4 architects like Doug Carmean which address that concern and make it seem like they have it under control. Many engineers at Intel (including the main Pentium 4 architects) must have known the problem was more dire than that. But everyone falls prey to wishful thinking, and changing the bearing of a mammoth ship is not something easily accomplished.

> Pentium 4 was absolutely the right design to take advantage of faster transistors

No, it was a horrible design in many ways, irrespective of those constraints and any wishful thinking about the power wall, and it gave the advantage to AMD for years. Not a big surprise as it was designed by Intel's B team. The Pentium M which has been the microarchitectural basis for their subsequent desktop processors was designed by the A team.

everyone falls prey to wishful thinking

To be fair, nobody has ever designed a CPU based on current process technologies. Design teams are always saying "we think the process technology we'll end up working with will look something like this...", and based on past history there was no reason to think that the power issue wouldn't get solved like it had the past N times.

I'm certainly not claiming I could have done better. But the Pentium 4 was such a spectacular failure and Intel's competition managed to navigate that transition well enough that I feel a certain amount of pointing and laughing is justified. :)

The good thing since then is that industry started focusing on power consuption. Maybe the "mobile revolution" wouldn't take place if they kept running for clock improvements at each and every project.

Yeah, but to get those they had to make a much less efficient architecture (the P4 required more clock cycles to do the same things). The Pentium M (CPU part of Centrino), which I believe became the Core, was based off of the P3 architecture, and was faster at something like 33% lower click speed. So those 3+ GHz P4s were kind of evolutionary dead ends. But man, was it exciting when they broke 3...

This was true of pretty much every CPU generation before the P4. Deeper pipelines result in lower FO4 (and thus higher attainable clock frequency), but a higher penalty for branch misprediction, among other things.

Historically (pre-P4) this was a great tradeoff. The Alpha 21064 was a barn-stormer; it ran at nearly twice the Mhz of its brainiac competitors at the time. This more than made up for a deeper pipeline and simpler execution units.

What killed the P4 was that they hit the power wall. Moore's law scaling of gate size no longer resulted in a corresponding scaling of power usage.

It is hard to blame the P4 designers too much for this, since people have been prophesying the end of Moore's law since the mid-80s at least. They happened to be designing when it actually happened on power. Current designers should look to that lesson when relying on increasing density...

Of course, these lessons are pretty useless, because much like a stock market bubble, Moore's law continues on a given metric until it doesn't. And it is always obvious in retrospect.

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