I have to say that overclockers pin special hopes upon AMD Energy Efficient processors, as they expect these CPUs to boast a much higher overclocking potential. It is pretty hard to determine what these expectations are based on, especially since Energy Efficient processors feature the same microarchitecture as their “regular” counterparts. And the stable operation at lower nominal clock frequencies and with lower Vcore doesn’t at all mean that it will work at sky-high frequencies if you increase its core voltage…
However, we couldn’t help checking out the overclocking potential of the processors that we got at our disposal. Athlon 64 X2 4600+ with the maximum heat dissipation of 65W was the first one we installed into our testbed.
The testbed was built using ASUS M2N32-SLI Deluxe mainboard based on Nvidia nForce 590 SLI chipset, Corsair Twin2X1024-8500 memory and PowerColor X1900 XTX 512MB graphics card. The processor was cooled with Zalman CNPS9500 AM2 air-cooler. Since the maximum clock frequency multiplier of the Energy Efficient processors (just like the “normal” ones) is locked, these CPUs can only be overclocked by raising the clock generator frequency. In this case we had to reduce the multiplier for the memory frequency and HyperTransport bus connecting the CPU with the SPP in order to ensure that all other subsystems of the test platform work stably.
Without increasing the core voltage, i.e. with 1.25V of power, Athlon 64 X2 4600+ working at 2.4GHz nominal speed could only overclock to 2.6GHz (and work stably at that frequency). The clock generator frequency in this experiment reached 221MHz.
The second overclocking experiment was conducted with the processor core voltage increased to the level of “regular” – not Energy Efficient – CPUs, that is to 1.35V. In this case we managed to raise the clock generator frequency to 232MHz without losing the system stability. The CPU worked at 2.78GHz in this case.
The third experiment was performed with the processor Vcore raised to 1.5V. This core voltage is 20% higher than the nominal value, and normally you should be concerned with arranging special cooling for the processor. However in this case it is pretty safe, because the Energy Efficient CPUs are manufactured using the same semiconductor dies as the regular processors, so the Vcore increase to 1.35V can be performed safely, as the potential of the die “allows” it initially. In other words, it makes sense to increase the core voltage basing on the nominal Vcore settings for the “regular” processors from the same family, rather than on the nominal Vcore set for the given CPU model.
We managed to get our processor to work at 2.84GHz core frequency while the clock generator frequency in this case equaled 237MHz. all further overclocking attempts to hit higher speeds resulted in instability, so we would consider the last result to be the maximum.
This way, Energy Efficient Athlon 64 X2 4600+ processor with the maximum heat dissipation of 65W could overclock only to 2.84GHz, i.e. its frequency potential didn’t surprise us. The regular CPUs of the same type with the 85W TDP could most probably hit the same mark during overclocking. In other words, our very first experiment indicated clearly that there will hardly be anything special about the overclocking potential of the Energy Efficient processors. However, it is definitely too early to make any conclusions. We still have one more Energy Efficient processor: Athlon 64 X2 3800+ with the maximum wattage of 35W and 2.0GHz nominal clock speed.
The nominal Vcore of this CPU model is 1.075V, so we didn’t really expect much without increasing this parameter. And our expectations were absolutely true: by simply raising the clock generator frequency we could only hit the 215MHz mark, which results into 8% overclocking to 2.15GHz.