Archive for Monday, October 1, 2001

In comparing computers, does megahertz really matter anymore?

October 1, 2001


— When insurance agent Yolanda Barba went shopping for a new home computer, she sought a faster system that could run more programs than her old PC.

A salesman told her the speed of the processor measured in megahertz or gigahertz is the best measure of performance. She bought the pitch and an 800 megahertz PC.

Now, Barba isn't so sure she made the right decision.

"It's slower than the ones I use at work. I should have researched it a little bit more," the Patterson, Calif., resident said. "In the end, you get what you pay for."

For years, clock speed has been a reliable yardstick to compare the performance of processors, the "brains" of a computer. Now, analysts say, faster chips do not necessarily perform better.

"It has become an increasingly poor predictor of performance over the years because there are so many things that affect system performance," said Nathan Brookwood of the research firm Insight 64.

Comparing Apples and

Clock speed defines time within the microprocessor, in cycles per second. It's the rate in millions or billions of ticks per second at which the processor performs its most basic functions.

But like the revolutions per minute of a car engine, the raw power can be harnessed in different ways. That's the role of the chip's architecture.

Starkly different designs have never been directly comparable. Apple Computer Inc., which uses PowerPC chips in its Macintosh computers, has long claimed its processors perform better than those designed with the dominant Intel architecture, even though PowerPC chips run at a lower speed.

For years, however, competing chips from Advanced Micro Devices Inc. and Intel Corp. shared similar architectures. A megahertz war erupted, with each company trying to top the other's highest frequency.

"Because the AMD chip and the Intel chip had similar designs, it still was reasonable to compare the two processors based on megahertz ratings," Brookwood said. "Even though it was not an ideal metric, it didn't give you the wrong answer."

All that changed late last year when Intel introduced a new architecture along with its Pentium 4.

Early versions of the Pentium 4 carried a faster clock speed yet underperformed AMD's lower-megahertz Athlon processors in tests involving some common business applications.

At the same time, the Pentium 4 outperformed the AMD in tasks involving multimedia, such as video editing. Intel also points out that overall performance will improve as more software is optimized for the new design.

"In the beginning of any architectural shift, you create the hardware and put it into the marketplace, and you work with software community to take full advantage of it," said Louis Burns, vice president and general manager of Intel's Desktop Platforms Group.

Though AMD was the first to reach the 1 GHz threshold with its Athlon series last year, it has since fallen behind in sheer numbers. The Athlon now tops out at 1.4 GHz, while Intel recently introduced a 2 GHz Pentium 4.

Not surprisingly, AMD is now downplaying megahertz, joining Apple in the dismissal of what has become known as the "megahertz myth."

A new paradigm

Executives say what matters is the number of instructions performed per cycle, as set by the chip's architecture. And, AMD claims, the Athlon executes more instructions per cycle than the Pentium 4.

"Performance used to equal frequency. Now, it's a combination of instructions per clock cycle times frequency," said Pat Moorhead, AMD's vice president of desktop and mobile marketing. "It's really a new paradigm."

Both Intel and AMD plan to keep pushing the megahertz envelope, and Intel maintains that the frequency remains a valid guide for consumers in addition to reviews and benchmark tests.

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