A Guide to Undervolting your Processor


Nowadays, one of the main focuses of enthusiasts is the processor's performance. In order to reach new heights of performance, many increase the voltage of their processor to its peak and increase the FSB until instability occurs. However, for the casual user, performance might not the most important thing in computing. What about energy efficiency? It's obvious that energy efficiency has become an important thing for many users; simply look at the new line-up of AMD processors with an "E" at end of the processor's model name, e.g. 4850E and 5050E, which have rather low wattage. In order to decrease the wattage of these processors, processor manufacturers simply decrease the voltage of the processor in comparison to the older processor (not to mention die shrinks). However, the truth is that the voltage may be decreased even further to a certain minimum, in the same way manufacturers do not tap the processor's performance (and so we overclock). This is called undervolting and even the end-user is able to do it. Now, energy efficiency has many implications that may be of interest to you. Not only do you save a few watts (even a dozen of watts) and so decrease your electrical bill in the future, undervolting may be quite handy for notebook users that want to increase battery life. Undervolting also decreases heat output, which will decrease fan noise, and this is quite handy for HTPC users. Another great thing about undervolting is that performance is unaffected.

PLEASE NOTE: Most undervolting software have not been updated to support many of the new processors from AMD and Intel. AMD K10 users will be lucky enough to use K10Stat, but anything newer than the Intel LGA775 will not be supported by any software (as far as I know). For users of newer Intel processors, you will most likely have to use the BIOS. In many cases, undervolting will not be possible because the BIOS does not support it, as is the case of many consumer laptops.


In order to undervolt your processor, there is a variety of software you may choose from:

1. RMClock: RMClock Utility. Products. CPU Rightmark

2. CrystalCPUID: Crystal Dew World - Software - CrystalCPUID

3. Notebook Hardware Monitor (for notebooks only): Notebook Hardware Control (NHC) - Homepage, Downloads, Help, Docu, FAQ, 

4. K10Stat (for K10 AMD processors only): 

5. BIOS: depends whether your motherboard allows for this option or not. If none of the software work and your BIOS allows for controlling the voltage of your processor, this would be the best option. Nevertheless, the BIOS only allows to set a single voltage for the processor.

Each of these software work quite similarly, but may work with some processor and not with others. Therefore, you will have to experiment with each to see which one actually works. However, RMClock will be used as a demonstration in this guide as it is the most complex.

Before we go though how to use RMClock, you will need a few tools and this will include:


2. CoreTemp: Core Temp

3. HWMonitor (optional): CPUID

4. Prime95: |MG| Prime95 25.7

1. CPU-Z allows you to view the processor model that you are currently using. In my case, it is an Intel T5750. You may search on the Internet for information regarding it, such as how other users were able to undervolt it and this will give you a hint as to how much your processor is wasting energy. You may visit a thread on SilentPCReview: Undervolting: how low can you go?. Also, CPU-Z reports the voltage of the processor (Core VID) and this will allow you to know whether the software you are using is truly decreasing the voltage of your processor. If one software does not decrease the voltage, simply choose another or you may find out that your processor is unsupported. In this case, undervolting via the BIOS would be your only option, if it is supported by your motherboard.

2. CoreTemp is a processor/CPU temperature monitor. It may also be used to verify whether the software being used is actually changing the voltage (VID) of your processor.

3. HWMonitor is a temperature, voltage and fan speed monitoring software. You may use it in order to observe the temperature of your processor. In my case, my T5750’s cores are currently at 39C. Knowing your processor's temperature is quite handy as it allows you to compare its temperature before and after undervolting.

4. Prime95 is a stress software that will compute various calculations in order to determine whether or not your system is stable. If Prime95 reports an error, your system is not stable and this might be caused by the voltage of the processor being too low. When you load the software, simply click "Just Stressing". The "Torture Test" that you should choose is the "Small FFTs".


Now, this is where the fun begins. The system that I will be using for this demo is a Dell Inspiron 1525 with an Intel Core 2 Duo T5750 and Windows Vista Basic 32bit.

Step 1: Download RMClock and install/extract it. When you execute RMClock.exe, you will be greeted with the "About" page.

Step 2: Navigate to the "Advanced CPU Settings" in the tree and select the "CPU type selection" of your processor (this step only applies for Intel C2D systems).

Step 3: Navigate to "Performance on demand" in the tree. Tick "Use P-stat transisitions "PST" and all the "Index" for both "AC Power" and "Battery". Do not forget to scroll to tick all the "Index".

Step 4: Navigate to "CPU info". Here, you will need to note down the "Startup" and "Maximal"'s "Reg. Vcore (VID)". The VID is the voltage of the processor. In my case, it is 0.9500V and 1.2500V respectively. Notice that the "Maximal"'s "Reg. Vcore (VID)" might be higher than the stock voltage of your processor. I suggest you check online to make sure, or you can simply experiment and see whether your temperatures are higher otherwise.

Step 5: Navigate to "Profiles" in the tree and select the VID you saw earlier. The startup VID should be given to the lowest "FID' and the maximal VID should be given to the highest "FID". In my case, 0.9500V was for 6.0x and 1.2500V was for 12.0x. The "FID" is the multiplier of your processor. It is the factor by which the FSB is multiplied by in order to give the clock speed of your processor.

Step 6: In the same window, select "Performance on Demand" for "Current" and "Startup" of "AC Power" and "Battery". Also, untick "Auto-adjust intermediate states VIDs". Click "Apply".

Step 7: Now, you will begin undervolting. Simply select the VID for the highest FID and decrease it a notch. Click "Apply". Verify through CPU-Z to see if the "Core VID" has changed (notice that the Core VID reported by CPU-Z might not be the same as the VID in RMClock. Core VID is the voltage actually being supplied to processor, whereas VID is simply the voltage that was to be supplied. The discrepancy might be caused by undervolting/overvolting because of the motherboard.)

Now load Prime95 and run a Small FFTs Torture Test for 20 minutes. During this time, Prime95 will verify for errors and will halt the test if it detects one. Instability can also be noticed from a random lock-up or a blue-screen if the VID is decreased by too much. Continue decreasing the voltage by a notch if the stress test is a success. In my case, the 12.0x had a minimum VID of 1.0875V. Also, do not forget to occasionally restart RMClock, or all your settings will be reverted back to stock.

Step 8: Once you have found the minimum VID of a FID, you will untick the Index of the FID that you were undervolting. And you will continue undervolting the next Index just like previously. In my case, I will undervolt 11.0x. Continue until all of the Indexes were undervolted.

Step 9: Note that once you untick an Index in "Profiles", even if you retick it, it will not be used to make the clock speed. Therefore, you will need to renavigate to "Performance on demand" and reactivate the given "Index".

Step 10: Once you have finished "Undervolting", I suggest running Prime95 for 5 hours for each Index in order to verify if the voltage being supplied to the processor is enough for stability. My sister took my laptop, so I cannot show you the results of my undervolting.

Step 11 (END): At this point, you may choose to let RMClock startup whenever you log into Windows so that it undervolts your processor as your had previously configured it. Navigate to "Settings" in the tree and select "via Startup registry keys".


As you can see, undervolting has huge benefits for my Dell Inspiron 1525. Not only did it decrease the CPU temperature by 7C on load, but it allowed the fan to spin in its low mode which allowed for a much quieter environment for computing! Furthermore, it was observed that the battery life had increased by nearly 20% on load. Notice that your results from undervolting may vary as no processor is made the same.

There you have it. I hope you have fun undervolting your notebook or desktop!



There are a few things that you may want to double check or know in your want to undervolt to the fullest.

1. The CPU's voltage must be set to Auto under the BIOS.

2. EIST (for Intel) or Cool 'n' Quiet (AMD) should be enabled under the BIOS (to be verified).

3. Undervolting software, such as RMClock and CrystalCPUID, may hit a "voltage" wall, in the sense that they may not be able to set the voltage less than a certain value. This is apparent for my Intel Pentium Dual Core E2160. Its stock voltage ranges from 1.2 to 1.3V.

Nevertheless, it can be supplied a voltage from 0.8V to 1.5V according to Intel. If your motherboard supports CPU voltage control under the BIOS and that you feel that your processor may undervolt lower than that "voltage" wall, you may consider undervolting even more under the BIOS.