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Innovations in C3 Processor Stepping

The new C3 stepping of the Deneb processor core will eventually come to other Phenom II CPUs, besides the top models. However, only the new processor stepping will bring lower TDP only to the Phenom II X4 965 CPUs. This can be regarded as indirect indication that C3 processor stepping doesn’t provide too much of improvement in electrical and thermal characteristics.

We measured the practical power consumption of the old and new Phenom II X4 965 and it clearly indicates that:

In this case we measured the power consumption along the 12 V power line connected to the CPU voltage regulator, which means that the numbers above include the power losses that occur in the mainboard voltage regulator too. Nevertheless, they are quite sufficient for comparative purposes. The processor temperatures in the table above was taken off the diodes inside the processor cores. We used Thermalright Ultra-120 Extreme processor cooler with Enermax Magma fan. The processor was loaded using LinX 0.6.3 utility. Cool’n’Quiet and C1E power-saving technologies were activated.

The obtained results show that under maximum workload the new Phenom II X4 965 processor with C3 stepping proves only 7-8 W more economical than the C2 processor stepping. And it is only half the difference between their calculated TDPs. In other words, we shouldn’t overestimate the role of the processor stepping in the practical heat dissipation and power consumption. At the same time we should note that a Phenom II X4 965 processor on the Old core we had in our lab is not so bad at all in terms of power consumption. Its nominal core voltage is 1.4 V, just like the core voltage of the new CPU sample we got for review. However, Phenom II X4 965 processors with C2 stepping and 1.45 V Vcore may show considerably higher practical power consumption.

Lower power consumption and heat dissipation are not the only improvements AMD engineers introduced in the new Deneb C3 processor stepping. They have also done some work on the memory controller integrated into the CPU, as it now has improved electrical stability when working with four modules. In reality it means that if there is proper support in the mainboard BIOS then the processors with the new stepping can work perfectly fine with four DDR3-1333 SDRAM modules. As for CPUs with C2 processor stepping, then could only work stably with four DDR3-1067 SDRAM modules, while faster memory could only be used in dual-module configurations.

The third improvement introduced into the new processor stepping deals with the way C1E power-saving technology works. As you know, this power-saving technology allows lowering the CPU frequency and core voltage in idle mode upon the command from the OS. Until now AMD processors didn’t have any hardware implementation of this feature and C1E work was emulated via Cool’n’Quiet technology. However, this algorithm first required special support in the mainboard BIOS, and second was pretty awkwardly implemented causing the performance to drop as soon as it got activated. Processors with C3 stepping have finally acquired hardware implementation of C1E technology. AMD engineers promise that now C1E can be activated without risking to experience any performance drops, because the transition into this mode and back occur very rapidly.

In reality things turn out not so rosy. The thing is that activation of C1E technology on Socket AM3 platform requires Cool’n’Quiet to also be enabled at least in the existing versions of the mainboards BIOS’s. Therefore, we can’t really appreciate the advantages of the C1E hardware implementation in the new Deneb core to the full extent. Cool’n’Quiet technology either with C1E or without it continues to lower the performance of AMD processors by about 3-5% independent of the processor stepping type.

To illustrate what we have just said we can offer you the results of SYSmark 2007 that emulates the user’s work in different real applications:

Therefore, at this point we can advise the owners of systems built around Phenom II processors only to disable Cool’n’Quiet technology and sacrifice the power-saving in idle mode if they want to achieve maximum performance levels. However, it is also important to point out that the performance doesn’t drop too much when the power-saving technologies are in fact active.

As for the “pure” CPU performance, it hasn’t changed with the introduction of the new processor stepping. C3 stepping of the Deneb core has no microarchitectural improvements that could increase Phenom II X4 performance to a new level.

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