AMD Phenom

Verdict: The Phenom 9500 is much better value than the Phenom 9600.

AMD has been issuing press briefings about its quad-core CPUs for almost a year now. Considering that AMD's first quad-core CPUs, from the Opteron 23-series, were only launched two months ago, this shows just how late AMD's quad-core offerings are. In fact, we only just managed to obtain samples of AMD's quad-core desktop CPUs from the Phenom series in time for this Labs test.

The Phenom series of CPUs are based on the same K10 (also known as Barcelona) architecture as used by the Opteron 2300-series. However, while those SMP-compatible CPUs only support registered DDR2 RAM, the Phenoms work with standard unbuffered DDR2. Phenoms are made using a new package, known as Socket AM2+. As they work at the same 200MHz HTT frequency as Athlon 64 X2 CPUs, they also work in any Socket AM2 motherboard with a suitable BIOS update. Theoretically, a Socket AM2+ motherboard should allow you to adjust the frequency of each CPU core separately, as well as adjust the voltage of the integrated memory controller. However, none of the Socket AM2+ motherboards we've tested so far provides these abilities.

Inside each Phenom are four cores. However, unlike a Core 2 Quad, which is essentially two dual-core dies sandwiched together on one package, each quad-core Phenom is made from a single die. AMD's approach to designing a quad-core CPU looks good on paper, as each core has its own independent 512KB Level 2 cache, unlike in a Core 2 Quad, in which each pair of cores shares a 4MB Level 2 cache. In addition, each Phenom includes a large 2MB of Level 3 cache that all four cores can use to store shared data. This means that threads that need to share data between cores should run faster on a Phenom than a Core 2 Quad.

However, this approach has several downsides. The most obvious of these is that if one core proves to be faulty during production, AMD has to throw away the entire die, whereas if one of the cores in a Core 2 Quad is faulty, Intel can just pick another dual-core die off the manufacturing line and finish assembling the CPU. As a result, Core 2 Quads are much cheaper to manufacture than Phenoms.

The Phenom series aren't AMD's first CPUs made using 65nm transistors, but it means that they should be a lot more power-efficient than the earlier K8 architecture CPUs, most of which were made using 90nm transistors. Apart from the new cache design, the K10 architecture offers a number of improvements over the K8 architecture. For example, the K10 architecture can handle up to four floating-point instructions per clock, features improved branch prediction, supports 128-bit SSE instructions and introduces SSE4a. The latter isn't to be confused with SSE4, which is supported by Intel's Penryn architecture Core 2 Extreme QX9-series CPUs.

AMD has plans to produce dual-core and triple-core Phenom CPUs but, at launch, only two quad-core models are available - the 9500 and 9600. Both models have the same cache architecture, so the only difference between them is that the 9500 runs at 2.2GHz, while the 9600 is clocked at 2.3GHz. A 2.4GHz model known as the 9700 was also due to be released now, but its launch was delayed at the last minute due to technical difficulties.

The Phenom 9500 is very similarly priced to the 2.4GHz Core 2 Quad Q6600. However, despite being nearly a year younger than the Intel processor, and having a theoretically superior true quad-core architecture, the Phenom 9500 proved to be very disappointing. For example, in our Media Benchmarks the Phenom 9500 scored 793, while the Core 2 Quad 6600 was much faster, scoring 1,036. The Core 2 Quad Q6600 was also much faster in other applications and games, with Supreme Commander running 43 per cent faster, while CineBench R10 and Folding@home ran 26 per cent faster and 23 per cent faster respectively. The Phenom 9500 draws less power than the Core 2 Quad Q6600 (240W as opposed to 244W) but, as it's so much slower than the Intel CPU, it's far less energy-efficient.

Despite being a brand-new CPU using a 65nm manufacturing process, we could only overclock the Phenom 9500 to 2.53GHz, while a B3 stepping Core 2 Quad Q6600 will usually overclock to at least 3.3GHz and a G0 stepping model to 3.6GHz, even with a standard HSF. As the Phenom 9600 runs just 100MHz faster than the Phenom 9500, it doesn't perform significantly better. As a result, it wasn't able to close the performance gap with the significantly cheaper Q6600 and is therefore best left on the shelf to rot.

It's taken AMD around nine months longer than expected to release Phenom - almost a whole life cycle in the semiconductor industry. If Phenom had been launched on schedule, it would have given Core 2 Quad a run for its money. However, as Intel has had nine months to rake in the profit as the world's sole supplier of quad-core CPUs, the company has been able to drop the price of Core 2 Quad without losing money. As a result, at today's pricing, it makes absolutely no sense to buy a Phenom 9500 or 9600, when a Core 2 Quad Q6600 is faster, and more power-efficient and overclockable.