When we finished this round of tests on Asus M4A78T-E mainboard, we put together a testbed around Gigabyte GA-MA790XT-UD4P in order to check if OCZ memory would work ok and see how far we could push our test processor here. As you know, the memory wouldn’t work, CPU overclocked way higher at the default processor core voltage, but the results of maximum CPU overclocking test remained exactly the same. We had to increase the CPU Vcore only to 1.525V, while the additional +0.15V had to be provided for the North Bridge controller integrated into the CPU.

We are going to discuss Gigabyte GA-MA790XT-UD4P in detail in our next review, and now at the final testing stage we are going back to our today’s hero - Asus M4A78T-E mainboard. We reinstalled the operating system and ran performance tests in the nominal mode as described in the previous part of the article. After that we launch the same set of benchmarks on an overclocked system, but suddenly the BSOD comes up during 3DMark Vantage run. It was very strange, because we reproduced exactly the same testing conditions as before. Tried to change a few things, but again no luck. Desperately looking for answers in the preliminary test results obtained on Gigabyte mainboard, and notice that it required higher voltage on the North Bridge integrated into the CPU to ensure stability. So, we increase this setting a little, then another bit and finally pass the notorious test. And things could have been great, however, the system could no longer pass the long-term stability check in Prime95.

By that time I was already a little exhausted by all the problems I faced since the beginning of the Asus M4A78T-E test session. However, I reduced the overclocking to a completely different reason. Asus M4A78T-E mainboard can send maximum 1.45V to the CPU by default. In order to be able to raise the Vcore to 1.65V, you have to reset the “CPU overvoltage” jumper on the board. We did this exact thing to ensure that we could overclock our processor to its maximum. However, we started to get “Overvoltage error” message pretty frequently on system boot-up. It required pressing F1 to continue booting. I didn’t pay too much attention to it for a while, but then I went into the Hardware Monitoring section. Although the system was working in its nominal mode and I didn’t raise any voltages, the CPU was getting over 1.64V! I immediately recalled that Everest often reported higher CPU Vcore when we ran the tests on an overclocked processor. Namely, it read up to 1.62-1.64V, although we had only increased it to 1.575V in the BIOS. Check out a couple of screenshots above. I assumed that it was a monitoring error, but turns out that the CPU was in fact receiving that much voltage. Could it be slowly killing our CPU thus affecting its overclocking potential? Well, we will find out during our Gigabyte board tests, and at this point we’d better give up “CPU overvoltage” function altogether.

I usually record my experiments in a special overclocker log. That is why I immediately remembered that at 1.45V processor core voltage the system passed LinX stability test at 270MHz clock generator frequency, but refused to restart. It would freeze in the very beginning, during the graphics card initialization process. At that time I thought that it happened because of overly overclocked processor and used “CPU overvoltage” jumper to raise its Vcore a little further. This time let’s try and lower the clock generator frequency to 265MHz – no restart. The same happened at 260MHz and only when we got down to 257MHz we could reboot the system successfully. However, this is relatively low frequency. Gigabyte mainboard could reach just a little lower frequency even with the nominal processor Vcore…

Well, there is a lot of stuff connected with the processor core voltage here, so I decided to try and lower it a little and see what happens. This was the right thing to do. Now the board could reboot at 258MHz clock generator frequency. After a couple of additional experiments I discovered that when the CPU Vcore is lowered down to 1.4V, Asus M4A78T-E mainboard can even restart successfully at 270MHz. That was almost a victory! I say “almost” because this voltage was not enough for the system to pass the tests at this frequency.

Finally, when the processor Vcore was at 1.4V, Asus M4A78T-E mainboard could only ensure satisfactory operational conditions for it at 250MHz. this is where we had to stop.

Actually, 250MHz frequency is very convenient for CPU overclocking. In this case we get nominal frequencies for the memory, North Bridge integrated into the CPU and HyperTransport bus. In fact, we increased the North Bridge frequency to 2500MHz and lowered the memory timings in order to pump up the speed.

Now we need to find a worthy rival for our test processor. From our review called “Meet Socket AM3: AMD Phenom II X4 810 CPU Review” we know that this processor can successfully compete against Intel Core 2 Quad Q8xxx series, however, I didn’t have a CPU like that at my disposal at the time of tests, unfortunately. Instead I had the new Intel Core 2 Quad Q9400 with yet unknown overclocking potential. Would you like to check it out now?

Luckily for us and unfortunately for the undertaken comparison, the CPU overclocked brilliantly. So far, I have never exceeded 500MHz FSB in my overclocking experiments on quad-core Intel Core 2 Quad processors.

Sadly, even when if overclocked AMD Phenom II X4 810 to 3.7GHz, it wouldn’t stand a chance against the overclocking monster from Intel. So, our 3.25GHz achievement is absolutely out of the question. Well, since we don’t have a fair rival at this point, we will just stick to on single CPU in the next round. It will give us another change to check out the advantages from CPU overclocking.

Not bad at all. We overclocked our CPU by 25% and got the same performance boost. Of course, lowering the memory timings and increasing the integrated North Bridge frequency helped achieve these results.