In articles past, talked a lot about the overclock, which can increase the performance of the processor without paying anything more for it. On the other side of the coin, we also have the option to make an underclock, purposely reducing the frequency of the processor, aiming to make it consume less power and dissipate less heat. Imagine the case of a small serverfilesystem, which is connected all the time just by reading files in HD and dispatching them across the network, or a user that the USA micro Apan to browse and rotate light tasks, for example.

Besides the economy in to the light, you have the possibility to have a quieter PC, because it may disable some of the extra exhaust and use a cooler with adjustment of rotation on the processor (that with the lowest clock will be almost the entire minimum turning time in the rotation).

In other words, the overclocking will increase the processor power in situations where this is important, while underclock reduces electrical consumption and noise in cases where the power of the processor is more than enough. Today, even low-cost processors, such as the Pentium and Celeron based E Conroe-L offer performance several times higher than that of processors a few years ago, which makes the underclock especially useful in HTPCs, small servers and PCs for the lighter tasks.

Add underclock is simpler than doing overclock, since you need only reduce the multiplier of the processor (remember, it is only locked for more), until the frequency it considers sufficient. AnAthlon 64 3000 + (10x 200 MHz), for example, may have reduced the frequency up to 800 MHz, using the 4x multiplier:

Another option is to reduce the frequency of the FSB, which results in a reduction in consumption of the motherboard and other components. In an old Sempron 2800 +, Socket A (which works to 2.0 GHz) for example, you can reduce the consumption of the processor in almost 30 watts reducing the frequency of the FSB of 166 to 100 MHz in the setup, which makes the processor will work at 1.2 GHz

You can also get an additional reduction by reducing the voltage of the processor (undervolting), to find the minimum value with which it is stable. As in the case of the clock, the voltage is always defined by the manufacturers with a good margin of safety so that the processor works stable in any situation. Although the percentage varies, you almost always see a reduction of 8 or 10% in tension without sacrificing stability.

In addition to make use proportionately less power transistors to switch state, reducing the voltage causes the gate leakage exponentially becomes lower, resulting in a further reduction in consumption. While a 10% reduction in frequency reduces the consumption of the processor also at 10%, a 10% reduction in tension has resulted in a reduction from 15 to 20% in consumption.

In other words, the gain to reduce the voltage is exponential, not linear. Combining the underclock and undervolt you may very well reduce the consumption of the processor by 50% or more. The greater the frequency of operation of the processor, the greater the gain to reduce the tension.

Another possibility is merely to reduce the tension, keeping the processor operating frequency in default. In this case, you can get a considerable reduction in consumption, keeping exactly the same level of performance. This can save a good value on electricity during the life of the PC and make your PC breaks most "green."

Both AMD on Intel using undervolting to produce low-power processors (like the processor and the AMD series and Core 2 Quad Intel S of the series), where the nuclei able to work very stable with voltages lower than the are selected during the normal production and sold at double the price. Making undervolt you can get a similar reduction of consumption, without putting your hand in my pocket.

Unlike overclock both the underclock when undervolt not affect the useful life of equipment.Rather, the use of lower voltages reduce wear and allow your processor to remain healthy longer.

The only problem is the question of stability, since a reduction over the processor can stop or make several errors when it is most required, so it is important to check the stability of each step, using Prime95 or a benchmark that emphasizes the processing. If the PC is able to run the test for 60 minutes or more without stop, you can assume it will remain stable in real situations of use.

Just like when you overclock, it's important to be patient, starting with a small reduction and to increase until the test is to hang or display errors. A good way to save time is to use the EasyTune (in the case of the Gigabyte boards), AI Booster (the Asus boards) or another utility to adjust the voltage and multiplier through the desktop, without having to restart at each step:

Unfortunately this is still a restricted class of applications to Windows, so it is useful to keep it in dual-boot during the tests.

Anyway, other than older processors, where the frequency and voltage of operation were fixed, almost all current processors (with exception only of the old Celeron models) use energy management systems, which reduce the frequency of operation (by reducing the multiplier) and the operating voltage when the processor is idle, providing an automatic reduction in consumption.

Monitoring the processor using the CPU-Z, you will notice that the fields' Core Voltage "and" Core Speed "vary with the load of processing:

And a Pentium E2180 (of 65 nanometers), for example, operates 1.2 GHz (6x 200 MHz) when idle and automatically switches to 2.0 GHz (10x 200 MHz) when nominal full-load, the voltage is adjusted automatically.

The values are recorded in the microcode and the processor automatically detected by the motherboard, but vary depending on the model or even according to the number of processors. That's why Intel does not disclose further tension "correct" operation of the processors, just to disclose a range of tensions within which the processors can work, as in the case of the Pentium E2180 goes from 0.85V to 1.5V.

As you can imagine, the voltage required varies with the frequency of operation. The processor can work with 0.85V when operating at a low frequency, but need to work stable at 1.35V overclock, for example. The 1.5V turn is the maximum stress that can be used safely.

You will notice that the voltage shown by CPU-Z is always a little below the voltage specified in the setup. The voltage of the E2180, for example, is 1.325V, but according to CPU-Z it does not exceed 1.280V at full-load. Reducing the voltage to 1.100V, it is only in 1.052V, 0.050V again around less.

This occurs because the voltage dropping, which makes the voltage of the processor is slightly below the nominal voltage when the processor is in full-load, a security measure to prevent the voltage exceeding the maximum voltage during the peak occurring when the processing load is removed. In other words, the voltage specified in the setup is only a limit, not a constant value. The advantage of monitoring the voltage using the CPU-Z is that it shows the real voltage, based on information provided by the monitoring circuit included in the processor.

The E2180's test, for example, has remained quite stable at 2.0 GHz with only 1.043V, which represents a reduction in consumption of 13 watts at full load (nearly 40% of total) without sacrificing performance:

By limiting the multiplier to 6x (making the processor operates at 1.2GHz all the time, no key to the 2.0 GHz), it was possible to reduce the voltage to 0.912V, which resulted in a reduction of over 12 watts, which essentially the E2180 turned in a ULV processor, which consumes little more than 9 watts at full-load:

For comparison purposes, it is only 5 watts more than an Atom 230 (which has a TDP of 4 watts), making it perfect for use in a HTPC or a small server that is connected all the time without making a lot.

In the case of the AMD processors, the Cool'n'Quiet is used, which reduces the frequency of operation of the processor to 800 MHz and 1.0 GHz according to the model, also reducing the tension.

In the case of the Phenom X4 II, for example, the default voltage is 1.37V, but you can almost always reduce it up to 1.17V without affecting its stability. It may seem little, but on a Phenom X4 II 955 (3.2 GHz), it results in a reduction in consumption of 35 watts at full processor load.

When the processor is idle, the Cool'n'Quiet enter into action, reducing the frequency to 800 MHz and the voltage to only 1.02V (0.960V in CPU-Z because of Vdrop), which is a very aggressive reduction, already made with the objective to minimize the consumption of the processor. The voltage at idle is independent of the voltage specified in the setup, so there is not much to do to obtain additional gains.

Another important observation is that the temperature affects the conductivity of materials, making the processor needs a higher voltage to remain stable at 60 ° than 36 ° the need, for example.

Thanks to this, you will make it easier to keep undervolt the processor is working to lower temperatures. Place a funnel in additional output of the back office of wind tunnel and on the processor, or simply leave open the cabinet can greatly improve the results.

As for the overclock, the undervolt is not an exact science. Each processor is different, so the results always depend on a certain amount of luck. You may have slightly different results even when using two processors in the same series.