Know Your Frequencies
To actually attempt to overclock a processor, you need to understand how the frequency domains work, and how the final clock is found. If you can multiply two numbers together, then you can figure this part out quite easily.
The slide above is actually a little bit more confusing than it is in practice. In general, you have a base clock (BCLK), and then you have multipliers; the final frequency for each domain (CPU cores, uncore/cache, and memory) is the BCLK times the multiplier for each domain. The BCLK is also the same frequency as the PCI-E frequency of the CPU's PCI-E lanes. This can prove to be cumbersome when dealing with PCI-E devices like GPUs, so Intel has provided BCLK dividers. The BCLK dividers are also referred to as Gears, and these can increase the final BCLK without you having to increase the PCI-E clock.
Here you can see highlighted values in the UEFI. The first section is for BCLK and it is boxed in blue. The final BCLK is the base clock/PCI-E clock of 100MHz (at default) multiplied by one of three gear ratios, 1.00x (default), 1.25x, or 1.67x.
The next values are in red, these are domain multipliers, and the final frequency of each domain is its multiplier times the final BCLK. In most cases, you just want to leave the BCLK untouched at 100MHz (100MHz x 1.00), the only reason to really use the BCLK gears is if you want higher DRAM clocks, since some boards are limited to 26.66x as their top DRAM multiplier at this time.
This is another shot of the frequency domains from one of Intel's slides.
On average, you might be able to pull of 105MHz on the BCLK/PCI-E base frequency, and on many boards all the dividers work, so most boards can do 175MHz (1.67x105).
A trick to help with higher PCI-E clock achieve 105MHz+, is to change PCI-E mode from 3.0 to 2.0, as PCI-E 2.0 allows for more variance in clock.
These are advanced CPU Core features. On the motherboard we used for this guide, we can just disable everything related to CPU power saving in the UEFI. Some brands require EIST be left enabled, some let you disable it, and they enable certain parts to allow turbo multipliers behind the scenes. This will be specific to each manufacturer.
If you want to ensure your CPU multiplier and voltage are reduce at idle, then enable the settings I have disabled above. I disable these things to maximize CPU stability and overclocks, but that is just how I am used to doing it. Enabling power savings will save you about 30W at idle and perhaps a few degrees at idle. Full CPU load conditions shouldn't change with them enabled, however, you aren't guaranteed your full overclock at much lower loads.
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