Underclocking my CPU

[philosofool]

I have moved an old Core i5 750 to work as a HTPC. Obviously, this is a very over-powered system for such a role.

I'd like to reduce the amount of heat that the system produces. What is the best way to do this? I assume it includes reducing CPU voltage and then finding stable BCLK and Multipliers, but I don't really have an idea how to start with this. Am I right to assume that TDP is a scalar function of CPU volatage? What is the low end of CPU volatage I might expect to opperate? Any advice is appreciated.

 

[Idontcare]

Underclocking is no different than overclocking in terms of methodology for verifying stability.

For starters, there is an easy, fool-proof, way of doing it but you don't get the maximum benefits. All you do is go into the BIOS and simply lower the CPU's max-allowed multiplier to whatever value you want and don't touch any other setting.

This will reduce performance (obviously), but it will also reduce power consumption as well as operating temperature. Reducing operating temperature has a two-fold benefit - it lowers the noise because the HSF is now quieter, and it further lowers power-consumption because the leakage current is dependent on temperature (and voltage, but you aren't touching that in this "fool proof" option).

If all you touch is the multiplier when underclocking then stability is guaranteed provided the chip itself was already stable at stock clocks.

The second option for underclocking is to further maximize the benefits of lower power-consumption and lower temperatures by way of optimized the CPU voltage. As your processor will be running slower and cooler, from reducing the clockspeed multiplier, it will also not need as much voltage.

So you can also lower the Vcore, and then stress test the same as you would an overclock to ensure it is still stable.

Lowering the Vcore will further lower the temperature, reducing noise and power consumption.

I don't have an i5 750, but here is an example of how low the voltage could go on my 2600K when underclocking: