After a long wait we’ve finally got our hands on AMD’s first consumer quad-core processor, the Phenom (previously codenamed Agena), and we’ve tested the fastest Phenom 9000 series processor, the 2.4GHz 9700 model.

It has four cores manufactured on a single piece of silicon, rather than Intel’s approach of two dual-core pieces of silicon in one package.

Each core has 512KB of L2 cache, with a shared 2MB L3 cache so data can be shared and processed effectively across the cores.

The Phenom has an integrated memory controller, which can handle DDR2 memory up to 1,066MHz. The independent link between the processor and the rest of the system, Hypertransport, has been updated to revision 3.

It runs at 3.6GHz, which equates to a bandwidth of 14.4Gbytes/sec on a Phenom, compared with 8Gbytes/sec on previous AMD chips. Individual cores have improved branch prediction and 128-bit floating point units to speed up maths-heavy applications.

On the energy consumption side, Phenoms have fully independent frequency controls for each core and dual power plans so you can run the memory controller at a different voltage from the processor.

Phenoms are backwards compatible with AM2 sockets, so in theory you can pop one into an older AM2 motherboard and performance will only drop by 10 per cent in the game Call of Juarez, according to AMD. In practice though, the four AM2 boards we had in our labs weren’t compatible with the Phenom, with the necessary Bios upgrades ‘pending’.

To get the most out of Phenom, you’ll want to plug it into an AM2+ socket that’s attached to AMD’s new 770 and 790 chipsets, which give you Hypertransport 3 and better power control.

So, on paper the Phenom looks impressive, but in our labs it struggled to keep up with Intel’s slowest quad core part, the Core 2 Quad Q6600.

A 3Dmark06 CPU score of 3,350 for the Phenom 9700 was bested by 3,577 with the Q6600. The Q6600 was also six and 12 per cent faster in Cinebench 9.5 and 10 respectively.

In gaming, the Q6600 just pipped the 9700. In Fear, both using a Radeon HD 3850, the Q6600 rendered 102fps, while the 9700 rendered 96fps.

Furthermore, we’ve reliably overclocked the G0-stepping Q6600 to 3GHz without a voltage tweak in our labs, resulting in scores similar to a high-end Core 2 Extreme. With the 9700, however, we couldn’t get above 2.5GHz without a voltage jump, although we believe higher speeds are possible when we get more time with it.

The Phenom’s native design didn’t achieve good energy efficiency either. It drew 120W when idling and 210W under strain, while the Q6600 system, with an X35 motherboard but otherwise identical components, drew just 88W and 171W respectively. The 9700 has a TDP (thermal design point) of 125W, while slower Phenoms (the 2.2GHz 9500 and the 2.3GHz 9600) have peak power draws of 95W, so there are power savings to be had at the lower end of the range.

If you’re planning on upgrading from an AMD dual-core system, think wisely before you choose a Phenom. If software isn’t optimised for four cores then a 3GHz Athlon X2 6400+ can be quicker. In our single-core Cinebench 9.5 test, the 6400+ was 13 per cent faster than the 9700. But in most scenarios we found the Phenom was considerably faster than the 6400+.

Just after we finished our initial benchmarking, we learned that there is a problem with the L3 cache that causes instability in some instances. Motherboard manufacturers are issuing Bios updates that improve stability by disabling part of the L3 cache's functionality.

We tested with a Gigabyte MA790FX-DQ6 motherboard, initially using the F2L Bios revision. We received Gigabyte's beta bios, named F3C, that fixes the TLB erratum problem, but performance fell using the new Bios.

3Dmark05 CPU score dropped to 3203, a drop of five per cent. Cinebench 9.5 dropped by four per cent, PCmark05 CPU test dropped by 1 per cent and Fear stayed the same (reflecting that this game is pretty GPU dependant).

Because of the buggy roll out, the Phenom 9700 has been delayed by a couple of weeks. Its pre-order price reflects its baseline performance - we’ve seen it on sale for £180-£200, but that’s still more expensive than Intel’s Q6600, going for £160 at the time of writing (early December).

We recommend holding off buying a Phenom until a new revision, rumoured due out in early 2008, is released.