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Phenom II: Unlocking Cores, Cache, And A Free Lunch

Tweaking For Stability

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.

Image 1 of 2

Unlocked X3 720, ACC Enabled

Image 2 of 2

Stock 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.

Image 1 of 2

Unlocked X4 810, ACC Enabled

Image 2 of 2

Stock X4 810, ACC Disabled

CPUs You Can Use

Results
OriginModel #Week/SteppingUnlockable
Phenom II X4 810 From AMDHDX810WFK4FGI0849 CPBWYes
Phenom II X4 810 From ASRockHDX810WFK4FGI0848 DPMYes
Phenom II X4 810 From NeweggHDX810WFK4FGI0903 CPAWYes
Phenom II X3 720 From AMDHDZ720WFK3DGI0849 CPMWNo
Phenom II X3 720 From ASRockHDZ720WFK3DGI0849 CPMWYes
Phenom II X3 720 From NeweggHDZ720WFK3DGI0904 EPMWNo

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.

Chris Angelini
Chris Angelini is an Editor Emeritus at Tom's Hardware US. He edits hardware reviews and covers high-profile CPU and GPU launches.
  • dirtmountain
    Good article. Now if you can just get your ad clowns from sticking us with those annoying ads.....!
    Reply
  • test them with games... some people care about that :P
    Reply
  • cangelini
    Well, but the point isn't the benchmarks. We already know that most games are going to be limited more by graphics horsepower versus whether a CPU has three or four cores/4MB shared L3 or 6MB shared L3.

    In fact, when it comes to gaming, you're going to be better off looking for the fastest overclock possible with your three good cores or 4MB of known-good cache, really.
    Reply
  • omg you replied to me... i'm so honoured :P

    but yes, i agree... but if you had crossfire gpus, this would make a difference. but then again, i think you'd have the money to buy the real thing (phenom II 920)
    Reply
  • tacoslave
    i like this article toms should do more stuff like this.
    Reply
  • apache_lives
    Page 3 "it ran for an hour sans error before we shut it down" - mistake?

    Me wonders if extra v's would help both to the memory, HTT and cores etc, or underclock that extra core if possible....

    On the other hand as all overclockers/modders should be aware THERE'S NO GUARANTEE on what you can get out of your hardware etc.

    Out of interest, is the third core ("Core 2"... LOL) still always the culprit of every X3 (unlockable or not)?

    Now if only there was some super secret on modding my Q6600 into a i7 940.....
    Reply
  • cangelini
    Hey Apache! No error, sans = without.
    Reply
  • apache_lives
    still reads wrong to me?
    Reply
  • Summer Leigh Castle
    Good article but can someone explain how ACC % works? Also, where do we start in terms of ACC % if we're tweaking for stability?
    Reply
  • ravenware
    cangeliniHey Apache! No error, sans = without.
    The only reason I know that is because of Wayne's World2.
    Reply