Intel i5-2500 3.3GHz LGA1155 Sandy Bridge CPU Review - Undervolting, Underclocking, and Overclocking

Undervolting and Underclocking

Undervolting and underclocking may seem like a strange concept at first, mainly why would anyone try to make your processor work below stock?  Although underclocking may have a more niche usage, testing underclocked configurations help us paint a picture of the relative efficiency of Sandy Bridge chips in their stock configuration.  Undervolting, on the other hand, is a bit like overclocking, but its aim is to maximize the efficiency of the chip at a given frequency.  Where would this become beneficial, you may ask?  Outside of being generally more efficient, and save some money on your electricity bill, the big gains come in the ever-growing folding/distributed computing projects which are often run 24/7/365, and the increasing cost of electricity adds further incentive to keep your chip running at the minimum power it can run in a stable fashion.


We will test the i5-2500 to see how low we can volt it, and keeping in mind that power draw is linearly related to the voltage at a given current, we can see how lowering the voltage helps in the power consumption of the processor.  Another aspect sought by undervolters is for passive, quiet, or media HTPCs who either desire minimum CPU cooling needs for acoustics or simply not having the room for higher-end cooling due to space limitations, and undervolting will also reduce the thermal output (thermal power) of the processor as the power load decreases with the undervolt.


Undervolting keeps the CPU frequency the same, which means you don't sacrifice speed, but you attempt to "feed" it the lowest power needed to keep it stable at that frequency.  This means it's using only as much power as it needs to operate stable, and optimizing the voltage is much like overclocking, with testing the boundaries, and then testing for stability.  Default or "auto" settings are intentionally conservative to ensure stability.  However, when overclocking, voltages become conservative in the other direction to protect against thermal damage, and both play a role in the overall flexibility of the platform.


We will also perform a quick overclock for power, voltage, and performance comparisons to visualize a better relationship between the various tests and relating them to the power required across a wider clock spectrum.



Overclocking on Sandy Bridge is a bit simpler than previous platforms, as base clock (BCLK) is not modified much.  Instead, it's mostly the multiplier which is responsible for changing the clock speed.  The "K" models offer an unlocked multiplier, and much greater overclocking potential.  The i5-2500 is able to clock two bin steps higher, to a maximum of 3.8GHz, which is easily reached without adjusting anything but the multiplier, which provides a nice 15% clock boost.  This presents a bit of a challenge to the i5-2500 chip, as it's currently only ~$10 cheaper thank the i5-2500K, and even if you're not planning on any overclocking which extends beyond the abilities of the i5-2500, the $10 is likely worth it for an overall more efficient and better slab of silicon.

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