Overclocking, Unlocking, And Heart-Stopping
Let’s start with the most interesting news first.
You’re probably not going to believe this—I certainly didn’t at first—but whatever AMD was doing to turn off one core (yielding the Phenom II X3 700-series) or 2 MB of L3 cache (resulting in the Phenom II X4 800-series), it’s doing the same thing to turn Deneb cores into Phenom II X2 processors.
In order to test this, we set aside the Gigabyte MA770-UD3P motherboard used for the rest of our benchmarks (which didn’t have an SB750 southbridge, and thus no ACC) and dusted off the old ASRock M3A790GXH/128M board used to explore this same subject a couple of months back in Phenom II: Unlocking Cores, Cache, And A Free Lunch. We didn’t update its BIOS at first for fear of applying the microcode that’d undoubtedly render the undocumented feature unusable. Not surprisingly, the board didn’t recognize the CPU, but it still ran without an issue.
I hopped into its BIOS, set Advanced Clock Calibration to Auto, restarted, and was floored to see CPU-Z reporting all four of the chip’s cores fully functional.
Not believing my eyes, I ran our MainConcept benchmark and came back with a time of 2:09—almost half that of a Phenom II X2 550 running at 3.1 GHz (as you’ll see in a couple of pages). Remembering back to the hit-and-miss stability of our last exploration, I fired up Prime95 and let it run for a couple of hours. Though not completely thorough, the fact that the test came back with no errors was still a shock.
Then came the moment of truth. Could we update the ASRock board’s BIOS to 1.10, updated back in April with new microcode, and still enjoy four cores? Yes, in fact, we could. Although the board’s most recent BIOS version still isn’t able to recognize the processor with four cores turned on, we were able to update and continue using the chip as what amounted to something in between the Phenom II X4 940 and Phenom II X4 955 with Cool’n’Quiet support fully supported.
Of course, just because our sample unlocked without a problem doesn’t mean that all—or any—others will. Who’s to say how representative of retail hardware an AMD-supplied processor will be? Then again, would AMD seed easily-unlockable chips deliberately, only to put something different out for its customers? I have to suspect not. More than likely, these dual-core Phenom IIs don’t bin as X3s or X4s. Some enthusiasts will simply get lucky and end up with chips closer to that line. So long as motherboard vendors aren’t forced to lock the Phenom II X2s out, we’ll likely see scattered reports of folks experiencing some success unlocking their processors.
The stakes are a little higher this time around, since we’re talking about turning a $100 CPU into a $220 CPU (averaging the 940 and 955 prices together). Back in the X3 720 days, you were looking at a $140 chip that might turn into a $190 model.
Kicking It Up
High off of our unlocking successes, it bothered us less that our Phenom II X2 550 wasn’t a particularly adept overclocker. With all four cores enabled, we were only able to push the 3.1 GHz chip up to 3.4 GHz before it petered out.
Once we disabled ACC, the ASRock board properly recognized the Phenom II X2 550 and we were on our way.
We managed to hit 3.8 GHz with it, but couldn’t lock in a voltage combination that’d run stably. Instead, we settled at 3.7 GHz and a fairly relaxed 1.4 V (Paul Henningsen was using settings as high as 1.55 V in his performance exploration yesterday).
There’s a definite performance improvement to be had from overclocking this CPU, but we’d much rather sacrifice the extra frequency for two additional cores at 3.1 GHz—especially in a test like MainConcept. While it’s true that you’ll get more speed in single-threaded apps by taking clock rate as high as possible, that’s of secondary importance given the speed-up in the apps optimized for threading.
