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4/7/2006
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Comparative Review: The Myth And Magic Of CPU Performance

When a 1.83 GHz Core Duo T2400 can outperform a Pentium 4 640 overclocked to 3.56 GHz, the world has turned upside down.

Pentium envy has been a driving force in computing for over a decade. When we hit 300MHz with the Pentium 2 in May of ’97 it was a major blow to plain old Pentium owners (not to mention slower Pentium 2 owners). I know this for a fact. I had one of the 300’s hot off the die and made sure to mention it whenever possible. If looks could kill . . . .

The Pentium 3 would have done the same for the P2 had it remained around long enough but suddenly — or so it seemed — there was a bigger, and even badder, Pentium 4. Even that didn’t last for long. Although Intel never launched the anticipated Pentium 5, the Pentium 4 continued to morph with mega amounts of L2 cache, Hyper Threading, and then dual cores. It only really stopped when Intel announced last year that the CPU would never see 4GHz.

Clock speed did go up some. My latest Pentium 955 Extreme Edition clocks at 3.46 GHZ and the last of the Pentium 4 royalty, the 965 Extreme Edition was released a short while later at a sizzling 3.73GHz. Then this Core Duo thing shows up. I’m not going to suggest that a Core Duo processor running at 1.83GHz could take down a dual core P4 965ee galloping along at 3.73GHz. It can’t, it won’t. (Admit it. For a moment you were worried, weren’t you?)

But how does all of that explain why 1.83GHz processor, even one with a dual core, can meet or exceed the performance expectations of a single core processor that’s clocked almost twice as fast? (Especially when that 1.83GHz processor resides in the undisputed land of lame, a portable computer.) The answer is chip architecture. It’s a solution AMD discovered a few years ago and Intel has been spinning it wheels trying to catch up with. It has now, although maybe not quite up to AMD levels yet, but even that is changing as we read.

The Pentium 4’s internal design was based around an architecture called NetBurst. The key features of NetBurst, according to Intel, are:

  • 20-stage execution pipeline: The Pentium III had only ten stages. By increasing the pipeline to 20 stages, Intel enables the processor to do even more optimization in the instruction flow. It also sets the table for some neat trickery Intel has announced for future chip generations.

  • A new cache architecture.

  • Double-clock arithmetic units: integer operations run at twice the processor clock speed.

  • Compact floating-point: faster operations of basic floating-point operations.

  • Streaming 128-bit arithmetic (called SSE-2): operations on multiple integer and floating-point values can be performed simultaneously.

  • Accelerated system bus.

Not included in this enumeration are smoke, mirrors, and a complexity of operation that practically demanded ever-higher clock speeds in order to provide ever-greater performance. While Intel could decrease the size of the processor dies periodically and thus simulate a speed increase (keep the same speed but shorten the data pathways, and data travels between points A and B in half the time — making it seem as if it had become twice as fast), each up-tick in real clock speed brought added heat to the operations and pushed the Pentium 4 closer to a meltdown. That’s why the wall was thrown up just shy of 4GHz. Flaming Pentiums are not good for public relations.

The cure, of course, was to take what was best from NetBurst, what was feasible from its mobility line of low power CPUs, add in any new skills learned in the last decade, and massage the mess into some new chip-level architecture that would emphasize performance without resorting to flames. That’s Intel’s new Core Architecture. Supposedly it will allow the Conroe series of desktop processors (the next one up for Intel) to leap 40 percent taller buildings while using half the power of current generation desktop processors.

Nice trick, huh? We’ll take a look behind the curtain to see what’s really going on next time.

Bill O'Brien can be blamed for more than 2,000 articles on computers and technology topics. With his writing partner, Alice Hill, Bill co-authored "The Hard Edge," the longest-running (1992 to 2004) technology column penned by a techno duo. For more, go to www.technudge.com.

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