Closer Look: AMD Athlon 64 FX-55

Released in June, the Athlon 64 FX-53 processor was targeting a rather narrow consumer group – extreme gamers. It has only one point of difference compared to the Athlon 64 3800+, the topmost model of the Athlon 64 family up to now – a larger L2 cache. This was supposed to continue further – a larger L2 cache remaining a prerogative of Athlon 64 FX series processors. But the just-announced Athlon 64 4000+ with 1 megabyte of L2 cache has brought about some confusion. The fact is AMD currently doesn’t have a core a CPU with more than 1MB of cache could be made out of. So, the company had to invent something different for the extreme gaming community.

Well, they just couldn’t be too choosy: all the capabilities of modern cores of the K8 architecture have long been realized in the Athlon 64 family. There was only one way out – a higher clock rate. As I mentioned above, the 2.4GHz clock rate of the Athlon 64 4000+ and Athlon 64 FX-53 is the limit of AMD’s capabilities both with old 130nm and the fresh 90nm tech process. But don’t forget that the Athlon 64 FX series includes premium products: such processors are expensive and are manufactured in limited quantities. When making them, the manufacturer can employ some methods that wouldn’t be economically profitable if employed for mass production of ordinary Athlon 64 CPUs. That’s how they found the solution: they just used some elements of their own 90nm technology to enhance the frequency potential of 130nm cores.

Particularly, AMD employed the so-called strained silicon in the 130nm process used to make Athlon 64 FX-55 dies (look here for details on this technology). Roughly speaking, they use this strained silicon in some critical spots of the chip, which limit the frequency growth the most (the 90nm tech process implies using such silicon everywhere in the chip).

This technology is rather expensive, but it allowed AMD to build something which had seemed impossible before: a processor with the K8 architecture, on the 130nm core and clocked at 2.6GHz. Thus, the difference between the Athlon 64 FX-55 and the Athlon 64 4000 is in 200MHz of the core clock rate. The rest of the formal characteristics of the Athlon 64 FX-55 are almost identical to those of the Athlon 64 4000+:

• Packaging: Socket 939;
• Clock rate: 2.6GHz;
• Memory controller: dual-channel with support of PC1600, PC2100, PC2700, and PC3200 DDR SDRAM;
• HyperTransport: one bus with a frequency of 1GHz (with DDR effect);
• Core: ClawHammer, manufactured with 130nm SOI technology;
• L1 cache size: 128KB (64KB for code and data each);
• L2 cache: 1MB, exclusive;
• Transistor count: 105.9 million;
• Core area: 193 sq. mm;
• Nominal voltage: 1.5v;
• Thermal design power: 108W.

Well, you may have noted another discrepancy in the spec above – a higher heat dissipation of the Athlon 64 FX-55. Yes, the increase of the clock rate above the previously intended limit without a transition to a more advanced manufacturing technology has pushed the power consumption and heat dissipation parameters out of the earlier set limits. The typical heat dissipation of the Athlon 64 FX-55 is 15 watts higher than that of the Athlon 64 4000+.

Considering the specifics of the Athlon 64 FX-55, our diagnostics utilities can report nothing sensational to us:

I should confess that the release of the 130nm Athlon 64 FX-55 processor is not as big a surprise as the arrival of the Athlon 64 4000+ on the old ClawHammer core. The transition of the Athlon 64 FX series to 90nm tech process had only been planned starting from the next model (supposedly, from the FX-57). So, I don’t find anything extraordinary in the characteristics of the Athlon FX-55.