There a few important voltages which you will need to manipulate while overclocking, below are the main ones. Not every motherboard BIOS is identical, but all enthusiast level motherboards should provide control of the voltages as shown below.
CPU Vcore – Directly related to the CPU frequency. As you increase the CPU frequency you would need incrementally increase the v-core as well. Bloomfield has proven to be extremely durable and I ran a number of Bloomfield CPU’s through the gauntlet and back with very high vcore. Everyone continues to ask what is “safe”, and I’ll continue my previous suggestion that a safe voltage for you system should be determined by your LOADED CPU core temperatures. So, while you are stress testing, monitor your CPU core temperatures with Real Temp and if the temperature is under control, you can SAFELY increase the voltage. So, the next logical question is what is a safe temperature, and Intel says 100C, and that’s what I go by.
Nothing I’ve ever used my computer for come close to generating heat like IntelBurnTest configured to use all threads. Because it generates so much heat, it has become my favorite stress testing application. As long as I can keep my CPU cores below 100C while running IntelBurnTest, then for me that’s safe. If you are more conservative/cautious than me that’s perfectly OK. IntelBurnTest at default will only spawn one thread for each physical core, so if you have HyperThreading support enabled on your CPU, please manuall select the number of threads in the drop-down box corrosponding to your CPUs thread count. From this point forward I will use the terminology IntelBurnTest (maximum) to remind you to manually configure the thread count if your CPU has HyperThreading enabled.
QPI/VTT voltage – This is the uncore voltage. Remember that the primary uncore devices are the L3 cache and the memory controller. This is also the primary adjustment required to increase bclock frequency. Again, for Bloomfield I personally wouldn’t hesitate to run mine up to about 1.45V on air 24/7. For Gulftown I don’t like to go over 1.4V for daily use.
DRAM voltage – This is directly related to your RAM modules and increases will allow increase in MEM speeds. There has been a lot of debate as to the limitation 1.65V limitation Intel has published. For quite a while users have been running much higher DRAM voltage without ill effect. The justification has always been that the default VTT is 1.15V and the DRAM voltage has to stay within 0.5V of the VTT. I have always played by that rule, although many power users have questioned whether it’s needed or not. Doesn’t really matter to me, because I usually run VTT at 1.3V minimum which would allow me to run DRAM voltage up to 1.8V without breaking the rule, and 1.8V is plenty for most memory on the market these days.
Whether or not it’s necessary I’m not going to debate here, but it’s an easy rule to follow, and it’s stood the test of time that you can safely run your DRAM voltage up to VTT +0.5V
I keep going back and forth with this guide trying to make it easy to read for everyone, and yet still relevant to anyone’s personal goal. Sometimes as I’m typing away, I feel like I’m over explaining things over and over and that it’ll cause more confusion than clarity. So, for clarity, as you read the guide, I’ll be referring to the following thee sample goals and hopefully that’ll allow my explanations to be a little more concise.
***This OC should be possible with the stock Intel cooler and minimal voltage increases***
***This OC will require high end air cooling at a minimum and moderate voltage increases***
***This OC may require water cooling or better and moderate to high voltage increases***
I would start by entering the BIOS and select “load optimized defaults”, then save and exit. After the reboot, go back into the BIOS and turn off the start-up slash screen, so that you can view your system’s post behavior. Also, feel free to disable any “integrated peripherals” that will not be used (i.e. NICs, extra PATA/SATA controllers, legacy devices, etc). All other overclocking settings you can leave on auto for now.
If you are looking for your maximum overclock, and you’re not concerned with power consumption, disable all power saving features. These include, but are not limited to; EIST, C1E, and all other C-states.
First you need to isolate the bclock, because all other major devices derive their frequencies from the bclock, it’s the logical starting point. In order to isolate the bclock from the other components, the first thing you need to do is manually force a low multiplier for the CPU.
Just like the CPU, the memory receives its clock from the bclock via a multiplier, in this case the default is 8 (133×8 = DDR3-1066). This is expressed in the BIOS as “8″. For now, we want to drop that down a bit.
In all sample system, the IMC is the limiting factor, and we don’t want to push it up yet, that is the reason for all three to be set at 6 for this step, don’t worry it won’t be there for long.
As previously mentioned, the uncore clock ratio must be set to double the System Memory Multiplier (SPD) with Bloomfield and 1.5 times the memory multiplier with Gulftown. In this step, set the uncore clock ratio based on your desired System Memory Multiplier (SPD) (not the temporary memory multiplier we’re using right now).
For this step, there are only two voltages you should play with; VTT, and IOH Core. IOH Core voltage is easy, if you are running a single PCIe card (graphics card), give the IOH Core 1.1V, two graphics cards 1.15V, three graphics cards 1.2V, or four graphics cards 1.25V. If you plan to run bclock frequencies far beyond 200MHz, sometimes it may help for the IOH core to be even higher.
As mentioned above, QPI/VTT is the crucial voltage adjustment for achieving high bclock stability. Default QPI/VTT is 1.15V and to reach 200MHz bclock you’ll likely need to increase this to at least 1.2V, many CPUs will require 1.3V or more. The only way to know is to follow the instructions here and find out.
For all three sample systems, start by setting the QPI/VTT voltage to 1.2V.
Go into the BIOS and set the CPU Clock Ratio, the Uncore Clock Ratio, and the System Memory Multiplier (SPD) to the setting we just decided on in the previous sections. Then go to the voltages section and adjust your IOH Core and your QPI/VTT voltages. Then restart your machine and go back into the BIOS, if your system fails to post, start a new thread in the forums and ask for some specific help. Please be sure to include as many details as possible when posting in the forums, and post a picture of the specific problem if possible.
After you’ve restarted your system with your manually configured voltages and returned to the BIOS, adjust the bclock speed from 133MHz to 150MHz. Then save and exit and allow the system to reboot. This time, allow the system to boot fully into the operating system.
Once the operating system has fully loaded, start up RealTemp. RealTemp should always be running while checking for stability of an overclocked system to ensure you do not overheat your CPU. RealTemp shows your CPU’s core temperatures real-time. Now start up CPU-Z, this utility will allow you to ensure that your overclocked settings have been properly applied, and that you are running at your desired speed. Check both the CPU tab for the expected CPU frequency, and check the memory tab to ensure your memory and uncore are both running at the appropriate speed. At this point the sample systems should each show up in CPU-Z with the following speeds.
***Note***, if you have SpeedStep (“EIST”) enabled, the CPU speed will fluctuate in CPU-Z when the load changes, please verify values given above WHILE RUNNING YOUR STRESS TEST.
Now start up your selected test program, for example OCCT (mix) or IntelBurnTest (maximum). Run the test for just a short amount of time, I usually try to run 3 loops with IntelBurnTest (maximum). Then reboot the system and return to the BIOS.
Continue to repeat this testing following the two procedures above, until you meet one of the following three criteria:
* Note – there is a phenomena known as “bclock holes” that may create confusion and frustration during this process. But if you appear to have found your limit at a much lower speed than anticipated, please consider trying a step or two higher before continuing on. A bclock hole cause’s system instability within particular bclock ranges, and going past them may allow you to regain stability.
After you have met one of the criteria above, you should have a rough idea of your bclock limit, now it’s time to get a little more fine tuned. So, revert back to the highest speed THAT PASSED the stress test. Then continue the same procedure as before, but instead of 10MHz bclock changes, shift to 2MHz changes until you meet one of the three criteria again. Also, ensure you check my note about “bclock holes” above, the same concept can be applied to this fine tuning step as well.
After you have found your highest stable speed to within 2MHz accuracy, lower the bclock by 2MHz and run your test again. This time let the test run for a full hour. If it passes the test - Congratulations! – you have found your highest reasonably stable bclock frequency. If it does not pass, drop the bclock 2MHz and attempt the full hour long test again, continue to lower the bclock in 2MHz increments until the one hour test will pass.
For the purpose of this guide, I’m going to assume you met the goal as provided in one of the 3 sample systems listed above.