How To Overclock A Clarkdale
As I mentioned before, I killed the previous Pentium G6950 in an overzealous overclocking attempt. After achieving reasonable load temperatures, I recklessly applied 1.475V to the processor, which is far too much for the Clarkdale-based CPU to handle, but enough to get it to 4.5 GHz. It worked for a while, and died during testing.
A more reasonable limit is 1.375V. That is exactly what we're setting the CPU voltage to in our current Pentium G6950 overclocking attempt, and the goal is to take it as far as that voltage will allow. With CPU Vcore set to 1.375V, the CPU Vtt set to 1.37V, the PCH core set to 1.16V, and the CPU PLL set to 1.9V, we'll see what this puppy can do.
I'm going to mention that the new Pentium G6950 sample we're using is a sample we purchased from Newegg, not some cherry-picked chip coming from Intel. Nevertheless, the CPU is ever-ready to overclock. It takes no effort to get this processor to 4.5 GHz with Prime95 load temperatures under 70 degrees Celsius. Of course, we have to keep things interesting, so we once again push the hardware past the point of reason.
At 4.6 GHz, the machine boots, but quickly crashes and damages the Windows installation while doing so. After a re-install, the machine still boots at 4.5 GHz, but the mouse does not work—it is likely that the chipset has been pushed past its limits. Stability is re-established with the system clocked to 4.3 GHz. Honestly, this is more of a reasonable overclock anyway, and we don't think there's much performance lost in those 200 MHz, but it's interesting to see that both of our Pentium G69500 samples made it to 4.5 GHz.
A final 4.3 GHz clock speed with low Prime95 load temperatures is fine by us. With a 205 MHz reference clock and a 2,870 MHz QuickPath Interconnect (QPI), that's an overclock of 1.5 GHz. This is certainly nothing to sneeze at, and if that doesn't wake up this CPU, nothing will.
With the Pentium overclock locked in, let's proceed to the Phenom II X2 555.
How To Overclock and Unlock A Phenom II Black Edition
Since we're using the same CPU and motherboard we did in our last review, we once again set the Phenom II's voltage to 1.5V, the multiplier to 19x, and the HyperTransport reference clock to 213 MHz, yielding a final dual-core overclock of 4.065 GHz.
But there is more work to do here. Our readers mentioned that they'd like to see if this processor can be unlocked--that is to say, can our dual-core Phenom II operate successfully with its two dormant CPU cores enabled? Can it become a true quad-core CPU?
To find out, you need a motherboard that supports core unlocking. Our Asus M4A785TD-V EVO motherboard supports this feature, so all we have to do is open the BIOS settings, enable Advanced Clock Calibration (ACC), activate Unleashing Mode, and select the number of CPU cores we want to activate. After activating all four cores to see if it would work and a quick reboot, we were rewarded with four usable CPU cores. The CPU won't overclock quite as high as it does with only two cores enabled, but comes close. With the multiplier set at 18x and the HyperTransport reference clock at 213 MHz, the final quad-core overclock is 3.8 GHz. It will be interesting to see if that 200 MHz clock speed deficit matters with twice the number of processor cores activated.
Since we were successful in our unlocking endeavors, I will mention that AMD provided our CPU sample. If you're planning to buy a Phenom II X2 555 just to see if all four cores will work, you probably owe it to yourself to do a little research about the success rate. In general, I don't like to test these kind of things in a CPU comparison because there are no guarantees, and there's no way for us to tell you how to identify an unlocked chip, short of trial and error. But our readers want to see it, and if a buyer knows the risks, there's no harm done. Do consider this a fair warning, though. There is no guarantee that the Phenom II X2 555 you purchase will successfully work with all four CPU cores enabled.
With our contenders ready to rumble, let's check out the test system's specifications so we can get things moving.