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Overclocking and Fourth Core Activation

45nm manufacturing process used to make Phenom II processors did help the company redeem their honor in the overclocking community. The statistics we have collected so far shows that with traditional air cooling these processors overclock to 3.6-3.8GHz frequencies. So far we haven’t experimented with overclocking of triple-core Phenom II processors, that is why we decided to devote some time to it within our today’s Phenom II X3 720 review.

We performed our overclocking experiments in the same exact testbed as was used for performance tests. I would only like to add that we used Scythe Mugen cooler with a Noctua NF-P12 fan.

Since this CPU belongs to the Black Edition series, we decided to overclock it by simply increasing the multiplier. At the same time I would like to remind you that as we have seen before, the alternative overclocking method by raising the clock generator frequency is just as good, too.

With the processor core voltage increased by 0.2V over the nominal (up to 1.525V), our test processor remained stable with 18x multiplier. We didn’t just increase the multiplier, but also raised the clock generator frequency a little bit, so the maximum frequency our Phenom II X3 720 reached during the experiments was 3.7GHz.

I have to remind you that Phenom II processors use an independent frequency for the integrated North Bridge. The nominal value for this frequency is 2.0GHz, but if you increase the corresponding multiplier to 11x and raise the NB voltage by 0.1V, you can push this frequency to 2.27GHz. We experienced no stability issues at this frequency.

As a result, we can say that the results of our today’s triple-core Phenom II X3 processor overclocking experiments fall within the statistics collected during the overclocking of the quad-core solutions. And actually, it is not surprising at all, because all Phenom II CPUs from AMD are based on the same semiconductor dies.

This is where we could put an end to our story about Phenom II X3 720 overclocking. However, we couldn’t miss the opportunity to check out if the recently revealed information about the way to enable the fourth core was true or false.

Unfortunately, we couldn’t get any of the AMD officials to comment on it. That is why we can only use our practical experience in investigating this matter. And our experience shows that the fourth core of Phenom II X3 processors can really be enabled, and if the particular Phenom II X3 processor is not based on an initially defective core, it may be turned into a fully-functional quad-core CPU. Therefore, it is fairly hard to estimate the probability of success for any core-activation attempts, because a lot depends on the batch the processor comes from and its production time.

In reality, CPUs may act differently during fourth core activation. Some samples simply won’t turn on in quad-core mode, some will start but will fail POST, some will fail only under significant computational load. We were lucky to get our hands on the best Phenom II X3 720 CPU that works just fine in quad-core mode and of course, we couldn’t miss this great opportunity to run even more tests.

The fourth core in Phenom II X3 processors can be activated very easily without any hardware modifications. All CPU computational cores will get automatically activated when you enable Advanced Clock Calibration (ACC) in the mainboard BIOS Setup.

It means that you will be able to activate all cores of your triple-core CPU only if your mainboard is based on an AMD chipset with SB750 South Bridge. The necessary functions are available in the BIOS of almost all mainboards built on AMD 790FX and 790GX. For our tests we used a Gigabyte GA-MA790GP-DS4H mainboard that enabled the fourth core of our Phenom II X3 720 processor in a wink.

Even though the processor model name was displayed in a slightly strange way during POST:

It worked impeccably in the operating system.

There is only on strange observation that I would like to share with you. During our tests with the fourth core activated CPU temperature monitoring stopped working. All diagnostic utilities reported that the processor core temperatures were 0°C.

However, it didn’t affect the system stability or performance in any way. Moreover, further experiments showed that quad-core Phenom II X3 720 could also be overclocked. The CPU was unstable at 3.7GHz that we had reached in triple-core state, but once we lowered the clock speed just a little bit, all stability issues were gone.

As you can see from the screenshot above, our triple-core Phenom II X3 720 worked stably as a quad-core processor at 3.67GHz frequency. Of course, this potential opens massive opportunities for those users who prefer to have their hardware run way beyond the manufacturer specifications.

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