Since the launch of Intel's first quad-core desktop processor over a year ago, there's been a conspicuous hole in AMD's product line up. But those days are over.

Phenom, AMD's crucial new quad-core desktop chip, has finally arrived. Is it good enough to keep Intel's latest 45nm quads honest? Or will the focal point for AMD's shortcomings simply shift from core count to pure performance?

Phenom-enal performance?

Unfortunately, the answer is largely the latter. Phenom shares its basic underpinnings with AMD's new quad-core Opteron processors. But it's not an all-new design. Rather, it's a moderate revision of AMD's existing K8 CPU architecture with the maximum core count taken up to four, plus a range of detail architectural enhancements.

The extra pair of cores aside, the most significant tweak is the doubling of floating point unit width to 128-bit. That allows all SSE-type 128-bit instructions to be handled in a single clock cycle rather than split in half and crunched two cycles. Intel's competing Core 2 CPU architecture has offered a comparable capability since mid-2006.

Similarly, Phenom's data fetch width has grown from 16 to 32 bytes, enabling it to fetch multiple instructions in a single cycle. Again, the idea is boosting clock-for-clock performance.

A range of further detail enhancements include the addition of HyperTransport 3.0 (only available when Phenom is used in conjunction with the latest AM2+ CPU socket) and DDR2 memory support boosted to 1066MHz, both in the name of increased bandwidth.

AMD has also bolted on a 2MB pool of Level 3 shared cache memory. This can be shared dynamically or monopolised by a single core according to workload requirements. Finally, Phenom packs the latest revision of AMD's Cool 'n Quiet power management technology.

The big news here concerns individual frequency control for each core and split power planes for the memory controller and northbridge on the one hand and the execution cores on the other. Both features give AMD more flexibility for minimising power consumption according to workload.

Elsewhere, Phenom sports essentially the same instruction pipeline and the 3-issue width design as existing AMD CPUs. The architectural carryover also means the memory controller and HyperTransport bus remain on-die. That's an enormous benefit in terms of bandwidth and latency, both of which are becoming increasingly critical in the context of data-hungry multi-core processors.