Perhaps the most common gripe about the Pentium 4's microarchitecture, called Netburst by Intel, was that its staggeringly-long pipeline was a gimmick ? a poor design choice made for reasons of marketing and not performance and scalability. Intel knew that the public naively equated higher MHz numbers with higher performance, or so the argument went, so they designed the P4 to run at stratospheric clock speeds and in the process made design tradeoffs that would prove detrimental to real-world performance.
I was one of the original dissenters from this school of thought, and in my P4 vs. the G4e series I tried to make a plausible technical case for why the P4's designers had made some of the design decisions that they did. I ultimately managed to convince myself and not a few others that the P4's deeply pipelined design was, in fact, performance-driven and not marketing-driven.
That was then, and this is now. As it turns out, the P4 bashers were right. Revelations from former members of the P4's design team, as well as my own off-the-record conversations with Intel folks, all indicate that the P4's design was the result of a marketing-driven focus on clock speeds at the expense of actual performance and scalability.
It's my understanding that this fact is pretty widely known within Intel, even though it's not publicly acknowledged. Furthermore, the P4's focus on megahertz has made it especially vulnerable to the industry-wide problems that have accompanied the 90nm transition, with the result that the new P4 probably won't scale very well at all in terms of both clock speed and performance. But I'm not going to say any more about the 90nm P4 problems, because I've addressed those elsewhere.
We now know that that during the course of the P4's design, the design team was getting pressure from the marketing folks to turn out a chip that would give Intel a massive MHz lead over its rivals. The reasoning apparently went that MHz is a single number that the general public understands, and they know that, just like with everything in the world except for golf scores, higher numbers are somehow better.
In the present article, which is the conclusion of my architectural history of the Pentium line, we'll take a look at the P4's Netburst architecture and at the sacrifices that Intel made at the altar of MHz. We'll then look at the relatively new Pentium M, before finishing off with a look at Prescott. If you didn't catch the previous article, be sure to read it first.
