Overclock ( Maximize Bclock Frequency )

overclock

Isolate the bclock from the CPU

First you need to isolate the bclock and find its stable limit with your chosen cooling.  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.  For example; at stock speed, an i5 750 runs on a 133MHz bclock and a x20 multiplier which results in its stock speed of 2660MHz (133×20).  Raising the bclock to 200 with the stock x20 multi would result in 4000MHz for the CPU, which you’re not quite ready for yet.  If you are shooting for a 200MHz bclock, then a safe choice for now might be a x12 multi, which would result in a CPU speed of 2400MHz if you were
successful in reaching your 200MHz target bclock.  Doing this isolates the CPU from the bclock so you can focus on only bclock overclocking in this step. In some situations, x12 may not work, this is just an example though, so don’t be afraid to try other low multipliers if x12 doesn’t work.

Isolate the bclock from the memory

The fastest rated speed for memory on P55 with an i5 750 (for example) is DDR3-1333, which is a clock speed of 667MHz (dual data rate “DDR” doubles the bandwidth to 1333-like speed).  Just like the CPU, the memory receives its clock from the bclock via a multiplier, in this case x5 (133×5=667).  This is most often expressed in the BIOS as “2:10″.  If you were to overclock the bclock to 200MHz as described before, your memory would be running at 1000MHz (DDR3-2000), and beyond the specs of all but the most extreme memory.  To isolate the memory from the bclock, lower the memory multiplier to the lowest setting available, most likely 2:6.  If you were to reach your goal of 200MHz bclcok frequency, your memory would only be at 600MHz (DDR3-1200) and well within the capability of all but the worst DDR3 on the market.

Isolate the bclock from the iGPU (Clarkdale only)

Clarkdale CPUs include an iGPU (integrated Graphics Processing Unit).  If you are using an H55 or H57 based motherboard and the iGPU is enabled, please pay close attention to this section. Some early BIOS versions did not allow for iGPU clock speed adjustment, if you do not have this option in your BIOS, please update your BIOS to the most recent version.  This platform is still very new and immature, so this information may only be relevant for a short time.  However, at this current time, it appears as though the iGPU frequency setting in the BIOS is based on the default bclock frequency.  This means that an iGPU frequency that is set at 900MHz in the BIOS, will only actually be 900MHz if the bclock frequency is set to 133MHz, if the bclock frequency was raised by 25% to 166MHz, the actual iGPU frequency would also go up by 25% or 1125MHz.  This is a relatively simple concept to understand, except that YOU have to do the calculation, because the BIOS only reports the set frequency, not the actual frequency.  What makes things worse at this time is that there is no software monitoring utility that is capable of reading the actual iGPU frequency.
For now, it’s only important to isolate it as a variable from our overclocking process.  So, assuming your goal is 200MHz bclock frequency, which is a 50% overclock of the bclock frequency, you need to lower the set iGPU frequency to prevent its overclock during this process.  If the stock iGPU clock speed is 900MHz and we were to overclock it 50%, that would yield a 1350MHz actual iGPU frequency.  To bring 1350MHz back down to 900MHz we would need to reduce it by 33%.  So reduce the set iGPU frequency by 33% to 600MHz, with our stock bclock frequency, the actual iGPU frequency would also be 600MHz.  However, if you successfully reach your target 50% increase in bclock, your set iGPU frequency will yield an actual iGPU frequency of 900MHz, which is the iGPU’s stock speed.

Bclock voltages

For this step, there are only two voltages you should play with; VTT, and IOH.  IOH is easy, if you are running a single PCIe card (graphics card), give the IOH 1.3V, if you are running more than one PCIe graphics card, give it 1.35V.  VTT is the crucial voltage adjustment for achieving high bclock stability, which is also known as “CPU VTT”, “QPI/VTT”, or “QPI/DRAM”.  This is the voltage that is fed to the IMC (Integrated Memory Controller), and also has a major impact in overclocking the bclock. CPU VTT is the crucial voltage adjustment for achieving high bclock stability.  Stock values differ depending on platform and CPU, but as a rule of thumb LGA1366 likes a lot, P55 doesn’t need as much.
So, are you ready to start overclocking?  After entering your BIOS and lowering the CPU & MEM multipliers, go to the voltages section and raise your IOH to 1.3-1.35V and your CPU VTT to +0.2V.  Then restart your machine and go back into the BIOS, if your system fails to post and return to the BIOS, please re-read the last paragraph in the “prerequisites” section above, and start over.  If you still cannot get past this step, post in the forums for some specific help.
After you’ve restarted your system with your manually configured voltages and returned to the BIOS, I always recommend going to the temp/voltage monitoring section and checking the CPU temp.  If the temperature seems too high for your cooling, then shut the system down and double check that your cooling system is properly mounted, and making good contact.  Moving on, almost all systems should be able to achieve 150MHz bclock stability with stock voltages, so go to the bclock adjustment and change it 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.

Testing for highest stable bclock frequency

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, as well as the distance to TJ Max, my advice is to never exceed TJ Max.  Now start up CPU-Z, this 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 (should be 1800MHz at this point), and check the memory tab to ensure your memory is running at the proper speed (CPU-Z will show the frequency of the memory, not the DDR3 speed, it should be 450MHz at this point).  Now start up your selected test program, for example OCCT or Prime95.  Run the test for just a short amount of time, five minutes should be plenty.  Then reboot the system and return to the BIOS.
If the test ran without error, raise the bclock by 10MHz, reboot into your OS and run the test again.  If the test failed, raise the CPU VTT voltage by a small increment, reboot into your OS and run the test again.  You should be able to see where this is going, continue to raise bclock or CPU VTT voltage with a short test after each change, until you meet one of the following criteria:

• You reach your desired bclock and successfully pass your stability test.
• You reach your maximum safe CPU VTT voltage.
• Raising the CPU VTT does not allow for additional stability.

* Note – there is a phenomena known as “bclock holes,” which seem to be less common now, but may still 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 causes system instability a particular bclock values, and going past them may allow you to regain stability.

Maximum safe CPU VTT

What is the maximum safe CPU VTT voltage?  Depends on a lot of things, but I feel like these are some basic conservative guidelines.  If you’re running the stock Intel heatsink and fan, I would not advise more than +0.2V, if you are running a high end air cooler I would not advise more than +0.3V on LGA1156 platforms, and no more than +0.4V on LGA1366 systems.  If you are running a high end custom water loop add another 0.05V to those values, and if you are using extreme forms of cooling then use whatever works best.  I’ve used up to 1.70V on an i7 920, and up to 1.55V with my i5 750 with extreme cooling.

Fine tuning

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.  Next, instead of 10MHz bclock changes, shift to 2MHz changes.  Then repeat the steps above and search for 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 it run for a full hour (for those of you testing with Super PI or similar, adjust for your situation).  If it passes the test  - Congratulations! – you have found your highest stable bclock frequency.