AMD Phenom Stockbridge GA

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AMD's first desktop quad-core CPU has had a difficult gestation. It was released almost a year late and, as yet, there are only two working models. The Phenom 9500 is a quad-core part running at 2.2GHz, the 9600 at 2.3GHz and the top-end 9700 gives the current top speed of 2.4GHz. It was originally slated to debut at 2.6GHz, but AMD's production issues have caused problems even with the 2.4GHz part. AMD, however, managed to get us a 2.6GHz part that's yet to be released. We also tested the mid-range Phenom 9500.

Power consumption

Being based on 65nm fabrication technology puts Phenom at a disadvantage. For a given clock speed, a 65nm transistor in a Phenom consumes more power than an Intel 45nm metal-gate transistor. That's not the end of the story, though: power consumption of a transistor is proportional to frequency, so Phenom's lower clocks are a bonus in that respect. And, all other things being equal, a CPU with a greater number of transistors consumes more power. A Phenom boasts a complement of 460 million, but an Intel Penryn quad-core part nearly doubles that, with an amazing 820 million transistors.

As with the Athlon 64 generation before it, Phenom processors are directly connected to main system memory by a dedicated on-chip interface. That means an AMD-based system doesn't need a separate north-bridge MCH (memory controller hub) and all its associated supporting components. From a "total-platform" power-consumption point of view this is a good thing.

But it does limit your choice of memory technology. AMD hasn't embraced DDR3 memory with the new part, and DDR3 support isn't slated to appear until the next-generation platform - currently codenamed Stars - arrives in 2009. Intel-based motherboards already have DDR3 support, bringing power-consumption advantages since DDR3's supply voltage is lower than DDR2, at 1.5V compared with 1.8V. That may not sound like much, but means a power reduction of 30%. Again, though, DDR3's higher clock speeds can offset the power savings.

Performance

As we saw last month with the 9500, the performance of Phenom leaves it trailing behind a similarly priced Core 2. In our test setup, using identical supporting components to the Intel rig, our overall benchmark result was 1.40; a good score, but far from stellar. A cursory glance at the specifications of the Phenom reveals why: just 4MB of cache in total, and a clock speed for the Phenom 9500 of only 2.2GHz makes it look a lot like a processor from a year ago as opposed to the cutting-edge design it's supposed to be. Phenom's novel three-tier cache structure means it's well set up for the future, though. With 512KB of cache dedicated to each core, new multi-threaded apps should benefit.

Value

The street price for a Phenom is impressively low for a brand-new part, but then it has to be to compete with Intel's price-slashing. The Phenom 9500 (web ID: 145203), at about £140, is competing with the faster Core 2 Quad Q6600. Prices have yet to be announced for the engineering-sample 2.6GHz Phenom we managed to get hold of.

Prospects

Since the launch of Athlon 64 in September 2003, AMD has traditionally launched an enthusiast-level FX part, countered by Intel with its Extreme-edition series. But with all the production problems afflicting Barcelona, there's no sign of them as yet. With its relatively low complement of cache making it unable to compete with Intel on that score, AMD desperately needs to improve its production to enable higher frequencies for better outright performance.

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Author: David Fearon

Phenom