The Phenom won't turn heads with its performance, but this 9900 model is a top upgrade option for users who already have AM2 socket-based AMD systems -- or is it? More on that later. It'll boost productivity and 3D rendering performance noticeably over a similarly configured dual-core Athlon 64 X2 and its four cores will supply extra venom over a dual-core Athlon when running more than two applications simultaneously.

We've covered the technological benefits of the Phenom before, so click on our review of the Phenom X4 9600 to find out how it differs from Intel's Core 2 offering; the 9900 does have a couple of differences compared to other CPUs in the Phenom family. Firstly, it employs a faster speed for its memory controller (2GHz, as opposed to 1.8GHz) and it has a faster full duplex HyperTransport 3.0 connection (4GHz, as opposed to 3.6GHz). That said, if you're in the market for a new PC, the Phenom's overall performance in today's productivity applications isn't likely to make you want to go the AMD route -- comparable Intel Core 2-based systems are still faster.

The Phenom 9900 runs at 2.6GHz, which is 300MHz faster than the 9600, and has four cores. A BIOS updated might be needed to get the CPU detected in existing AM2 socket-based motherboards. We had trouble getting the CPU to work on an older ASUS motherboard -- the M2N32-SLI, which uses the NVIDIA nForce 590 SLI chipset -- so AMD's claims of the Phenom being an easy upgrade for existing users haven't been proven by us yet. The CPU did work on the ASUS M3A32-MVP and Gigabyte GA-MA790FX-DQ6 boards, and we used the latter for our testing.

Running at its default speed of 2.6GHz, the Phenom 9900 scored 97 in WorldBench 6, which is about 8 per cent faster than what the Phenom 9600 CPU scored with an identical supporting cast of hardware. In the iTunes MP3 encoding test, it recorded 1min 15sec, which is 9sec quicker than the 9600 CPU, and in the Cdex MP3 encoding test it recorded 1min 39sec, which is 15sec faster than what the 9600 CPU could muster.

When we overclocked the 9900 to 2.86GHz, its performance scaled well. The extra 260MHz achieved an overall performance boost of 7 per cent, which is only 1 per cent less than the advantage gained when going from 2.3GHz to 2.6GHz (8 per cent). Our test platform remained stable at 2.86GHz, but it wasn't capable of going much higher. We used the standard AMD cooler for our tests, so we're not complaining.

For 3D rendering, we pulled the CPU frequency back to 2.6GHz, and the 9900's performance proved to be competitive. It was able to render four simultaneous threads in the Blender test in just 41sec. This is identical to the rendering time that an Intel Core 2 Quad 6600 CPU (which has a 2.4GHz clock speed) achieved running a comparable hardware configuration.

To produce these performance results, the 9900 will consume more electricity than the 9600; AMD states 140W for the 9900, which is about 40W more than the 9600.

The Phenom 9900 will command a much higher price than the 9600 so it's really aimed at users who want to perform taxing tasks, such as 3D rendering, in the least amount of time.