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Tweaking For Stability

Phenom II: Unlocking Cores, Cache, And A Free Lunch
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With the CPUs we confirmed functional, ACC was left to Auto in the ASRock board’s BIOS. The X3 720 sent to us by ASRock worked well through all of our benchmarks at that setting, laying down numbers illustrating the benefit of a fourth core. Then we ran the system through Prime95 to ensure stability. Only a few minutes in, the platform locked up and after a reset, it was only reporting three cores—even with ACC turned on.

This is a behavior we’ve read about, where a processor’s unlock wouldn’t “stick.” Fortunately, this gave us the opportunity to figure out how to get these unlocks, which sometimes fail, back into place.

Unlocked X3 720, ACC EnabledUnlocked X3 720, ACC EnabledStock X3 720, ACC DisabledStock X3 720, ACC Disabled

We started by taking ACC off of Auto, enabling the All Cores option. Moving in 2% increments, we were finally able to get the fourth core back on at -6%. And whereas it didn’t last long at all in Prime95 previously, it ran for an hour sans error before we shut it down. Surely, it seems that getting more aggressive with ACC has the potential to stabilize an unlock that’s “almost there.”

ACC won’t work miracles, though. On the two Phenom II X3 720s that wouldn’t work, we moved up to +12% and down to -12%, never seeing any sign of a fourth core.

Unlocked X4 810, ACC EnabledUnlocked X4 810, ACC EnabledStock X4 810, ACC DisabledStock X4 810, ACC Disabled

CPUs You Can Use

Results
Origin

Model #

Week/Stepping

Unlockable

Phenom II X4 810 From AMD

HDX810WFK4FGI

0849 CPBW

Yes

Phenom II X4 810 From ASRock

HDX810WFK4FGI

0848 DPM

Yes

Phenom II X4 810 From Newegg

HDX810WFK4FGI

0903 CPAW

Yes

Phenom II X3 720 From AMD

HDZ720WFK3DGI

0849 CPMW

No

Phenom II X3 720 From ASRock

HDZ720WFK3DGI

0849 CPMW

Yes

Phenom II X3 720 From Newegg

HDZ720WFK3DGI

0904 EPMW

No


The results look good for AMD’s Phenom II X4 810—and it doesn’t seem to matter when the CPU was manufactured or what its stepping might be. In all three cases, our locked 2MB of cache were made available by the ASRock board.

Unfortunately, the situation isn’t as rosy for the Phenom II X3 720. Only the “guaranteed” CPU from ASRock worked, and even then, it took some additional coaxing to make stable. Notice that our AMD and ASRock chips are from the same week and stepping; one unlocks and one doesn't.

Overclocking: Possible To Hamper?

There’s one more factor to take into consideration here. If you turn on a fourth core or previously-disabled cache, are you shooting yourself in the foot as you try to overclock from there? After all, those X3s and X4 800s are supposed to have faulty pieces, right?

We took the one Phenom II X3 720 that successfully unlocked and tried our hand overclocking it with Thermalright’s Ultra 120 Extreme. Our methods were simple—we stuck with multiplier adjustments and moved in 100 MHz increments.

With ACC turned off, the X3 720 ran Prime95 for an hour at 3.3 GHz before we shut it down (3.4 GHz would crash almost immediately).  Using the same voltage and 16.5x multiplier, we tried the same thing with ACC enabled and all four cores cranking. It didn’t take long at all for that fourth core to spit up an error, forcing us to scale back to 3.2 GHz for a stable run.

As you can see, the side effect of getting that extra core is a less fruitful overclock. In a single-threaded app like WinZip, you’ll see performance drop as a result. Just something to keep in mind.

Let’s see what prying the lid off of an extra 2 MB of L3 cache or a fourth core really get you, if you’re lucky enough to have a CPU that works.

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