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Value processors shatter the gigahertz barrier


Duron vs. Celeron at 1.1GHz
— 2:36 AM on October 1, 2001

THE LAST TIME we checked in on the value processor market, AMD had just released its Duron 1GHz processor, beating Intel to the symbolic 1GHz mark yet again. Since then, Intel has passed the 2GHz mark with its high-end Pentium 4 chip, and the company has quietly made available 1.0 and 1.1GHz versions of its Celeron value processor. AMD counters today with the release of its 1.1GHz Duron processor, which recaptures clock speed parity in the value market for AMD.

Performance-wise, the Celeron certainly needed the clock speed boost to bring it up to par. The 1GHz Duron absolutely crushed the 900MHz Celeron in our last round of tests. Let's dive into the strange world of value processors and see how the performance picture looks today.

The value processor equation
Value processors are an interesting anomaly that has shown up in the market over the past few years. Back in the day, we used to just buy CPUs off the lower end of the clock-speed scale in order to save a buck. Alternatively, we'd just buy a high-end 486 instead of a Pentium, or whatever the flavors of the day were. Thanks to the emergence of sub-$1K computers and the like, Intel saw a need to differentiate their high-end products from their low-end products a little more clearly. The Celeron—and thus the "value processor" segment—was born.

Intel and AMD have employed a couple of tricks in order to keep the value processors from nibbling into the market shares of their older siblings. That's important, because the chips are based on the exact same technology as those siblings—the Duron is a modified Athlon, and the current Celeron is a modified Pentium III. Among those tricks:

  • Shrinking the L2 cache — This trick neatly lowers the clock-for-clock performance of a processor, so that, for instance, a 900MHz Duron will generally perform slower than a 900MHz Athlon. Both the current Celeron and Duron have about half the on-chip cache of their big brothers. We'll get a visual look at the effective data cache size of these processors below, in our Linpack tests.

  • Keeping clock speeds low — If the time comes when you can find a 900MHz Duron on store shelves, odds are good AMD isn't actively producing 900MHz Athlons for sale any longer. To keep their products neatly segmented, processor makers have typically avoided making "value" and "mainstream" processors available at the same clock rate.

    Of course, this strategy hasn't always worked well; to this day, I have two Celeron "300A" processors (rated at 300MHz) running at 504MHz in a dual-processor system. Generally, if big brother can run at a given range of clock speeds, little brother probably can, too. So we overclockers like to keep an eye on the value segment, because we sometimes find hidden treasure there.

  • Using older bus speeds — Value CPUs get to ride on the older, slower front-side bus speeds most of the time. The Celeron only made the transition from a 66MHz bus to 100MHz earlier this year. The Duron's much better off here; it rides on a 200MHz bus, while newer Athlons sit on a 266MHz FSB. The slower bus speeds help ensure that these chips' smaller L2 caches are effective in reducing clock-for-clock performance. Taken together, a smaller cache and slower bus can really slow things down.

  • Using cheaper (and slower) memory types — Let's just say value systems aren't packed with DDR memory or RDRAM. The name of the game here is keeping things cheap and not too fast, and standard ol' SDRAM serves that purpose well. It's quite possible to match up a Duron or Celeron with DDR SDRAM or even, in the Celeron's case, RDRAM, but system builders don't spec value systems like that.
Because of these things, buying a 900MHz Duron instead of a 1.1GHz Athlon isn't quite the same proposition as buying an 800MHz Athlon instead of a 1.1GHz Athlon. In some ways, these value chips perform worse than their bigger brothers, but in others, they are faster—and sometimes, more advanced.

For instance, we've already explored how the new Durons, at 1GHz and above, are based on a revised version of the Athlon, code-named Palomino. The "Palomino" Athlons aren't available on the desktop quite yet, but their Duron counterparts, code-named Morgan, are. The "Morgan" Durons have a number of enhancements that increase their clock-for-clock performance, including logic that preemptively fetches data into the L2 cache and support for Intel's SSE multimedia extensions. In our last round of tests, the 1GHz Duron ran neck-and-neck with a 1GHz Athlon that lacks these enhancements.

So all we can say with certainty is that buying a 900MHz Duron instead of a 1.1GHz Athlon is kind of like buying an 800MHz Athlon instead of a 1.1GHz Athlon. The price and performance differences may be similar, but they won't be exactly the same. In this weird world of mutant processors intentionally engineered to run slower, that's about as good as we can do.