Phenom: Pros And Cons
If AMD had not had such a bad start with Phenom, people would probably be complimenting AMD for its Phenom quad core (based on the Agena core). The CPU provides solid performance and is clearly faster than an Athlon 64 X2 processor when compared per core or with all cores, especially if applications are thread-optimized. This means that workloads are split into smaller units, so they can be distributed across all available processing units to benefit from the available processing power. We also looked at the efficiency (performance per watt) of older and current AMD processors, where Phenom did really well too.
Even so, Phenom is not capable of competing with Intel's Core 2 Quad processors at current clock speeds of only up to 2.3 GHz. Intel, by way of comparison, is currently offering mainstream dual core processors at up to 2.6 GHz, with enthusiast Extreme Edition parts running at up to 3.2 GHz. And the new 45 nm Yorkfield-based quad cores are still to come.
But let's get back to the design. Phenom has 2x 64 kB L1 cache and 512 kB dedicated L2 cache per core, and there is a 2 MB shared L3 cache that can be used by all the processing cores. This is similar to Intel's approach with the Core 2 family, while Intel decided not to introduce a L3 cache and provide a larger L2 cache to two processing cores instead. Since Intel uses two Conroe or Wolfdale dice (65 and 45 nm Core 2 Duo) to create a Core 2 Quad processor (65 and 45 nm Kentsfield or Yorkfield), the Core 2's L2 cache is only be shared among two cores, causing traffic on the Front Side Bus that interconnects the two physical pieces of silicon. Looked at by design, AMD provides the better quad core, but judging purely by results, Intel still beats the living hell out of AMD. This is because its approach is economical and efficient, and - unlike AMD - it seems to have a solid grip on its manufacturing processes.
Where Intel typically requires an updated platform to run the latest processors (despite using the same physical processor socket), AMD announced that Phenom would be an excellent upgrade option for existing Socket AM2 systems, as the interface is backwards compatible. When we looked at BIOS support of ten different, 12+ month old Socket AM2 enthusiast and mainstream motherboards, we were disappointed to see that Phenom support was virtually nonexistent. However, two months have passed since we last looked, and we're going to look into this again. Until then, we recommend looking at AMD's recommended motherboard list if you want to be on the safe side.
A lot of discussion has been going on in popular forums regarding a possible bug in core 2 (the third) of the Phenom processor, causing Windows blue screens even at stock speeds. The topic can be found in our forums as well as other such as Xtreme Systems, and even on AMD's forum on the company website. There are more resources on the web, including AMD statements denying knowledge of a possible malfunction.
We've used three different Phenom processors in our labs, and none of them have been really good overclockers. We've had motherboard compatibility issues, but we weren't able to trace the described issues back directly to an individual core. And to me it doesn't really matter much anymore. It's really important for AMD to get its homework done right this time, and to present the highly anticipated B3 stepping, which is expected to fix the bugs and also introduce faster clock speeds. Nothing else will help to rebuild the trust that has been lost.
