Basic Concepts of Overclocking Intel Core i3/i5/i7 CPUs

Optimize Memory Frequency

DDR3 Basics

The next step is to find the limit of your memory. To do this, first you need to look at the memory’s ratings. DDR3 does not typically have a lot of overclocking headroom, so it’s important to start with stock settings. In this example I will use some basic Crucial Ballistix PC3-12800 for my explanations. This memory is rated for DDR3-1600 (800MHz) 8-8-8 24 1T with 1.65V. Enter the BIOS and adjust your memory timings according to the manufactures rating, in this case 8-8-8 24 1T. Now, consider your maximum/desired bclock frequency, 200MHz for example. This memory has a stock speed of 800MHz, so a 2:8 ratio with a bclock of 200MHz would put us right at that stock speed of 800MHz. You could set it and leave it there, but let’s say your maximum/desired bclock is not 200MHz. For example, if you are actually trying to reach 210MHz. If that were the case, the resulting memory frequency would be 840MHz (DDR3-1680). So, similar to finding bclock stability above, we need to work our way up to the desired speed testing along the way. There is an exception to this section, and that is with Clarkdale base Core i3 and Core i5 CPUs. They tend to have a very weak IMC, and are often times not capable of running memory even at their stock speed. If you have a Clarkdale based CPU, you may have to sacrifice memory speed to attain a good CPU overclock.

Testing for highest stable memory frequency

Theoretically we should be able to run for at least an hour with the bclock at 200MHz and the memory multi at 2:8– why? Because we already found out that this bclock speed is 1 hour stable, and we are not overclocking the memory yet.

However, the integrated memory controller (IMC) is powered by the CPU VTT voltage. So under some circumstances, especially with the newer 32nm CPUs, you may not be stable with your memory even at stock speeds due to the overclock imposed on the IMC. This is particularly true if you are running 4 DIMMS (P55/H55/H57), 6 DIMMS (X58), or 4GB DIMMS (P55/H55/H57/X58). If this is the case keep the memory at stock speed, or even try dropping the memory clock multiplier to run at less than stock speed, and increase the CPU VTT voltage until you gain stability. The newer 32nm CPUs seem to have particularly weak IMCs, and often will not run at the higher multipliers even if your memory is perfectly capable.

For testing memory, it is important that you take a break from whatever stability test you’ve been running, and use memtest86+ instead. The easiest way is to download the .iso and burn it to disc. Then configure your BIOS to load from your optical drive before the hard disk drive. When you boot the system with the disc inserted, memtest86+ should start automatically, and immediately begin testing your memory.

But, our goal is to reach 210MHz bclock, which will result in 840MHz memory frequency. In the BIOS, set your bclock to 202MHz, and your memory multi to 2:8, save settings and exit. Allow memtest86+ to load and complete one entire loop. A single loop can vary in length, and can take quite a while if you have a large amount of memory installed. If the test ran without error, press Ctrl-Alt-Delete and enter your BIOS. Raise the bclock by 2MHz and then save and exit. If the test failed, raise the memory voltage by a smallest increment possible, and run the test again. You should be able to see where this is going. Continue to raise bclock or memory voltage until you meet one of the following criteria:

  • You reach your desired bclock and successfully pass a single loop of memtest86+
  • You reach your maximum safe memory voltage.
  • Raising the memory voltage does not allow for additional stability.
  • Maximum safe memory voltage

What is the maximum safe memory voltage??? This is determined by two things:

  2. how much do you enjoy killing your memory? Throughout recent history, memory is probably the easiest component to damage with extra voltage. While there are exceptions, most newer DDR3 memory modules do not need very much voltage to reach their practical limits.

Once you have satisfied one of the three criteria above, drop the bclock down 2MHz from your last stable setting, and see if memtest86+ will run through 2 or 3 loops without error. If you wish to try to push your memory even further at this point, there is one more thing to try, and that is another bump in CPU VTT voltage. This will possibly boost the capabilities of the IMC and give you a little more room to overclock the memory. Otherwise – Congratulations! – you now have a relatively stable bclock frequency and memory frequency.


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