Undervolting The AM2 Processor

A couple weeks ago Legit Reviews was able to take our AMD Athlon 64 X2 4200+ AM2 processor and overclock it on air and water with amazing results. After this article was published we sat back and realized that we forgot about those readers who are looking to under volt their processors. With Home Theater PC's (HTPC) taking off many computer users are looking to reduce the voltages to save power and lower thermal temperatures of the processor and ultimately the case. Even if you don't care about temperatures undervolting your processor is a way to save energy and that means lowered energy bills!  Today Legit Reviews takes the same processor we overvolted to reach an amazing 3.1GHz thanks to water cooling and go the other direction.  Today we undervolt  the same processor and try to find the lowest possible voltage the processor can run still stable at with the hopes of lowering power consumption and system temperatures.

AMD 4200+ AM2 Undervolting

Starting out at the factory settings we ran the 4200+ AM2 processor at 1.35 Vcore and observed the temperatures and power consumption and idle and during 100% CPU load.  We then strarted lowering the voltage on the core down to the point where  the system became unstable.  Once we found where the system became unstable we were able to increase the voltage back up till it became 100% stable.

Image Description

Let's get started!  Here is a CPU-Z shot with everything on the motherboard set to 'auto' meaning default settings.  The vCore is set at 1.35V, but CPU-Z and other software utlities like SpeedFan detect the voltage as being roughly 1.232.

Setting The Voltages

To undervolt the processor the process is very simple and only one BIOS setting needs to be changed to undervolt just the processor.  After hitting the delete key while the system was posting we were able to get into the BIOS.  After going to the System Voltages page, under advanced settings, we were able to reduce the CPU voltage from 1.35V down in whatever we wanted thanks to the 0.025V adjustments found in the Foxconn BIOS.

Changing The BIOS

While lowering the voltage on the processor we ran stability tests to make sure the processor was 100% stable at these lower voltages. We ran a combination of stability tests, but stuck mainly to 3DMark2006, Super Pi and Prime 95.  A quick and simple way to test stability of a dual-core AMD X2 processor is to run two instances of Super Pi at one time.

Changing The BIOS

We also ran Prime 95 overnight and many Super Pi tests to 32 million places while doing other activities on the desktop to make sure the test system was rock solid.

Changing The BIOS

After running our test system through 72 hours of torture testing we came to the conclusion that 1.125V Core was the lowest voltage the core could do with 100% stability.  At 1.100V the system would crash while stability testing and at 1.075V Windows XP Professional coudln't get past the splash screen.

The Test System

Our Test System

The Test System

For testing we used the same platform that we used to watercool our AMD A64 X2 4200+ AM2 processor and only changed the processor voltages in the BIOS.  

What's Inside The Case?

Ultra UPS Test Platform



Live Pricing


AMD A64 X2 4200+ AM2


Foxconn C51XEM2AA


2GB Corsair PC2-6400C4

Video Card

2x BFG Tech GeForce 7800GTX 512MB

Hard Drive

Western Digital 250


Corsair Nautilus 500

Power Supply

Corsair HK620W PSU

Operating System

Windows XP Professional

To get an idea of the power consumption of our system and monitor we used our Seasonic PowerAngel meter and plugged just the computer system power cable directly into the meter.

Power Consumption and Temperature Results

After finding out the lowest stable voltage that the core could run at we used our Seasonic Power Angel meter and measured the total system power consumption in Watts. To get the idle results we let the system run at idle and then for load we ran Prime 95 and Super PI Mod v1.5 to ger the CPU running at 100% load.

AMD 4200+ Power Consumption

At idle we found undervolting the processor reduced power consumption by 11 Watts and under full load the power consumption dropped 28 Watts. By undervolting our processor we were able to save nearly 30 Watts of power under full load! 

What does that 30 Watts mean to you in temperature?  

AMD 4200+ Temperature Chart

When it comes to temperatures we used SpeedFan to monitor the core temperatures of the processor during our idle and load testing.  At idel the lower vCore was able to drop the core temperatures 2C, while at full load it droped 6C! With 100% system stability we were able to shave 28W and 6C off our system when it's under full load!  Not bad at all for just changing one setting in the motherboard BIOS (can also be done on nTune).

Final Thoughts and Conclusions

AMD 4200+ AM2 Undervolting

The AMD Athlon 64 X2 4200+ "Windsor" Socket AM2 processor keeps on impressing us and is really one of the most versatile processors that we have seen on the test bench in some time. While undervolting is not nearly talked about as much as overclocking I have a feeling more people are interested in it than overclocking.  If you think about the average computer user they use their computer to check e-mails, talk on instant messenger, watch videos on You Tube, and stalk old friends on MySpace! For users that do nothing more than that undervolting will reduce temperatures and power consumption, thus reducing noise levels and putting money back in your pocket. 

What power savings are you likely to see by undervolting your processor? Electricity is measured in kilowatt-hours and the current charge for electricity varies from state to state.  Since pricing varies from state to state and during seasons let's just use $0.14 per kilowatt-hour for pricing to figure up some rough numbers. Our testing showed that we were able to shave off 28W at full load, so let's see what that means in the real world.

Power Savings Estimates:

Since I keep my computer on nearly 24 hours a day and run Folding @ Home for the Legit Folding team I can expect to save over $34 a year by doing nothing more than undervolting the processor on my computer. While $34 might not be a lot to many people it's money that stays in your pocket and $30 is $30 if you ask us! 

Undervolting proved susscessful as we were able to reduced temperatures and lower the total power consumption on our test platform.  It almost makes you wonder why more people aren't doing this! In terms of pricing the cost has gone down a bit again and one of these processors can be picked up for $179 with free shipping over at Zipzoomfly! That's five dollars less than last week! For a processor that cost well over $330 last month it's now a bargin thanks mainly to the competition from Intel's recently launched Core 2 Duo series of processors.

Legit Bottom Line: Undervolting your processor is simple to do and it can help reduce system temperatures and lower your monthly electric bill for just a few minutes work.