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Need help with undervolting Phenom II 955

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December 8, 2009 10:44:30 AM

Hi all, I need some feedback / help on undervolting my Phenom II 955.
I will describe the methodology that I am following below, please let me know if I am on the right path / what I can expect / what I can do better.

1. System configuration is in my signature

2. Disabled Cool and Quiet in the BIOS

3. Downloaded HWMonitor 1.15, IntelTestBurn V2.3 and K10Stat 0.91 and opened all of them

4. Set the processor to P0 state (3200 MHz, 1.35V default)

- Using K10Stat, reduced the CPU voltage by one step (12.5 mV, I think)

- ran IntelTestBurn on Standard settings for 5 iterations (this is the default). Just for the P0, I also ran High for 10 iterations.

- max CPU temperature was 52 C, idle is 32-35C, ambient is around 20 C

- repeat

I could get it down to 1.2125V. At 1.2V, programs started to crash, and I saw display corruption. Interestingly, this screwed up something, and from the next boot, the CPU temperature was showing as 0 C! I had to reflash the BIOS to get back proper CPU temperature.

So now I think that 1.225 V (one step more) is the lowest I can go.

5. Set the processor to P3 state (800 MHz, 0.975V default)

- Using K10stat, force the CPU to 800 MHz, now reduce the voltage by one step

- I am currently running this (0.875V was stable, now testing 0.86V)

My questions are:

1. Is this a good / optimal methodology?

2. I assume I have to repeat this for the other two p-states as well (I think I will set the frequencies to 1600 MHz and 2400 MHz)

3. How do I permanently set these up, once I have the final settings?

Thanks for your inputs.
December 8, 2009 11:20:22 AM

Why would you want to underclock a 955?
December 8, 2009 11:26:19 AM

iZZ said:
Why would you want to underclock a 955?


To reduce the power consumption?

I mostly use this machine for gaming, and 3.2 GHz is more than sufficient to run all games at high settings (1680 x 1050).

Plus, it's just cool, in more ways than one :-).
Related resources
December 8, 2009 11:30:23 AM

Just to be clear, I'm not looking to underclock, rather to undervolt.
December 8, 2009 11:38:40 AM

so what your trying to do is starve the cpu of juice?? that is a quad core, dual cores can run on such low voltage but a quad will just crash as its trying to keep 4 cores stable, the default voltage is fine for this cpu @1.35v. (its default for a reason)
an amd is not an intel that can drop its core speed automaticly and nor is it going to make it drain alot less power.
your theory does seem pointless.

with my board i had to undervolt as my cpu was getting to much power, my board was feeding 1.31v to my cpu which is ment to take 1.26v so i manually set it in bios, the minimum my cpu can take is 1.1v but why would i want to run it that low to the point its barely powering it?? pointless.
December 8, 2009 11:47:59 AM

well if you get a voltage drop in the psu rail..,,, for example when your graphics card starts to kick in when playing a game, thats all it could take to make the pc lock solid as the little spike of a voltage change will cause instability if the core voltage is at bare minimum.
that 0.875v is the minimum to get the cpu to work not run efficiently, think of it like a 2-stroke engine, not enough oil it will seize solid when a load is put on it.
December 8, 2009 12:41:32 PM

I do get your point, although I don't agree.

To me, if a processor has headroom for overclocking, then it surely has headroom for undervolting as well, that's how the physics underlying it works.

The default voltage is only the worst case, there is no question of starving if the system runs fine at a given voltage. To me, this is free power savings, so why not take advantage of it?

In any case, I'm not going to debate this point - let's just take it that I want to reduce my electricity bill (which is poised to go up by 35% next month :(  ).

Do you have any feedback on my methodology / approach? Is there a better way to do this?

a b K Overclocking
December 8, 2009 2:36:42 PM

Hehe, by undervolting the CPU you will not notice any difference on your elec. bill. Ondervolting is useless unless you are running an HTPC setup or you have CnQ enabled to use the least amount of energy possble. You purchased a quad, quads are normally purchased when the user needs all 4 cores. If you wanted a lower elec. bill and you are inclined to undervolt you should have gone with a low TDP dual core CPU or at low TDP quad like the x4 620 ;) 
December 8, 2009 4:55:01 PM

"3.2 GHz @ 1.225V, 800 MHz @ 0.9V "
im surprised you can even start the pc with that ram voltage
i cant see the voltages going any lower as it will just cause problems
you should be happy that you have reached them lower voltages
if you wanted such lower power consumption just build a low power rig as ive done that runs on a 250w psu (still dual core).
also the lower the voltatge the more strain on the vrm's that are trying to resist and burn off the excess voltage, either way you aint doing the pc any favours or going to save enough electric to make it worth while.
a b K Overclocking
December 8, 2009 5:01:01 PM

I dont see the point of "power saving" with a rig that has a 955 and a 5850....
December 9, 2009 7:27:56 AM

pkw4 said:
"3.2 GHz @ 1.225V, 800 MHz @ 0.9V "
im surprised you can even start the pc with that ram voltage


Hmmn, perhaps I was not very clear in my original post. Let me try and explain again.

I am looking (mostly for fun) to find the lowest values at which my processor will run. Normally, I use Cool and Quiet. It runs at the below settings, each of which is called a p-state (by K10Stat).

Frequency Voltage Lowest Voltage
3200 1.35 1.225 (tested)
2500 1.25 1.1750
2100 1.15 1.10
800 0.975 0.85 (tested)

Note that the RAM voltage (1.6V) or the NorthBridge voltage (1.1V) are not touched at all.

The idea is to optimize Cool and Quiet, so that I can still get the same performance (since no frequencies have been reduced), at lower voltage. Once I have this, I want to set it permanently.

While searching for the lowest voltage, I need to disable Cool and Quiet, since it will never let me force the system to lower frequencies while running a stress test. During normal operation (like writing this post now), Cool and Quiet is enabled (and system is at 800 MHz - browsing does not seem to need much CPU).

I hope this explains what I am trying to accomplish. Thank you for all your inputs so far, all feedback is much appreciated.
a b À AMD
a b K Overclocking
December 9, 2009 2:24:01 PM

Don't be dissuaded. While the power saving may be negligible, as an intellectual exercise this is no different than an overclocker pushing in the other direction. For saving money, there may not be much you can do. Buying a 905e or 705e would amount to spending dollars to save dimes.

Edit: Oh, and a 4850e doesn't have the oomph to play games very well.
December 18, 2009 11:22:21 PM

@ QuadraticAmoeba

I totally understand what you are doing since I have done the same but for thermal reasons and not power consumption. At the end, power and heat problems get solved.

Here are my numbers:

3000 1.275
2100 1.075
1600 1.000
400 0.6625

I am running a 720BE with an unlocked 4th cores. My benchmarks' scores are equal or better than a 940 at the same clock.
December 19, 2009 2:08:06 PM

Thanks xsever. I didn't get too much time to work on this, but here is where I am now:

Freq Voltage
3200 1.225
2400 1.075
1600 0.925
800 0.775

How is the system at 400 MHz - what can you do with it? If you can browse and listen to music, that might be good enough for me at that state!

Someone told me that you could assume a roughly linear relationship between voltage and frequency. Based on that, I assume your 1.6 GHz could reduce a little bit. But, I'm just getting started on this stuff, so you may be a better judge than me :-)

I still have to figure out how to set this on startup - I tried putting K10Stat in a startup task, but it didn't work.

Anyway, on with the optimization!
December 19, 2009 5:30:18 PM

You will be surprised what the system can do @ 400 MHz. I can browse + listen to music + Windows Live Messenger + Everest + Ultramon ( for dual monitors) running. A video on youtube requires the 1600 frequency. When I game, I switch the power setting in Win 7 (through a shortcut - Executor) to High performance and this locks the CPU @ 3.0 GHz.

The voltages I posted are the minimum I can reach. I tried one notch lower for 1600 and it ended up with a BSOD. I am satisfied with the performance-on-demand concept!

As for auto-starting it, I use a software called Executor, which is a very handy launcher btw, that launches K10Stat with it.

Let me know how it goes.
December 25, 2009 5:14:22 AM

QuadraticAmoeba said:

I still have to figure out how to set this on startup - I tried putting K10Stat in a startup task, but it didn't work.


You have to specify a few command line options to make it work. Here is mine for example: "C:\Program Files (x86)\K10STAT\K10STAT.exe" -lp:1 -StayOnTray -ClkCtrl:2 -nw

-lp:1 --> load profile 1
-ClkCtrl:2 --> enable clock control (enable your custom p-state), use control function no 2 (ganged based on highest load core)
-nw --> no window (minimized on start)
-StayOnTray --> does what it says

Hope that helps.
December 25, 2009 10:19:10 AM

Thanks, that worked!
I did manage to get the 800 MHz down to 0.74V, so I'm all set now.
December 27, 2009 12:52:15 PM

Nice accomplishment. I was wondering how you have your up% and down% configured.

Please let me know.

Thanks,
December 28, 2009 4:08:23 AM

xsever said:
Nice accomplishment. I was wondering how you have your up% and down% configured.


Hi, I have not yet enabled ClkCtrl in K10Stat. I am running with default Cool and Quiet settings, but with a custom profile loaded. I tested each voltage/frequency individually using IntelTestBurn and then set them in the profile.

When I next get some free time, I will try the ClkCtrl - if you have some specific settings that you want me to test, let me know.

Thanks.
December 30, 2009 1:28:52 PM

Me too I do not use ClkCtrl. I just have the clocks and the voltages customized/optimized. I can see the processor shifting from a state to another other normally. Not really sure how ClkCtrl would change anything.

Anyhow, if you have more in-depth knowledge about the software, feel free to share it since the documentation is horrible.

Thanks,
a b K Overclocking
January 8, 2010 6:09:29 AM

Thanks for data! I've been looking into undervolting and I haven't gotten around to fixing my voltages to the lowest I can get them.
January 9, 2010 12:11:26 PM

kokin said:
Thanks for data! I've been looking into undervolting and I haven't gotten around to fixing my voltages to the lowest I can get them.

All the best!

I got good results using a linear approach - change in frequency proportional to change in voltage. Fix the two ends (3200 and 800 MHz in my case), and you can compute the intermediate voltages (for 2400 and 1600 MHz in my case).
a b K Overclocking
January 9, 2010 7:53:29 PM

That's not too bad for undervolting. Not exactly the best or good, but maybe a little above average. This is the best undervolting I have seen. While yes it is an overclock and not a undervolt centered test, it was running well under the voltage most other 550's require for just a 4 ghz clock. Same processor that hit 6.7 ghz on LN2.

http://www.xtremesystems.org/forums/showthread.php?s=e1...
a b K Overclocking
January 9, 2010 8:50:52 PM

AsAnAtheist said:
That's not too bad for undervolting. Not exactly the best or good, but maybe a little above average. This is the best undervolting I have seen. While yes it is an overclock and not a undervolt centered test, it was running well under the voltage most other 550's require for just a 4 ghz clock. Same processor that hit 6.7 ghz on LN2.

http://www.xtremesystems.org/forums/showthread.php?s=e1...

Nice link! Although those are unreleased & handpicked C3 chips, so they are gonna perform much better than any retail C2 chip.
a b K Overclocking
January 10, 2010 3:58:14 AM

kokin said:
Nice link! Although those are unreleased & handpicked C3 chips, so they are gonna perform much better than any retail C2 chip.


I have no doubt they were handpicked, although AMD will deny it.

I have already contact AMD to see if they will be released and if so when.
January 11, 2010 10:52:40 PM

I keep my 955 undervolted at 1.175. Toms ran a little test on this a while ago and they said it was the lowest stable at 3.2Ghz, and they were right. It also lowers the temps about 5-6 C idle and load.
a b K Overclocking
January 11, 2010 11:36:05 PM

I received the email from AMD tech support that they are not in the loop when they will be released but he noticed some retailers backordering them already.
January 13, 2010 8:51:23 PM

Having the ability to optimize the CPU's efficiency is awesome (from an Electrical Engineering point of view at least). I really like performance on-demand.

Glad to have you guys in the thread. Feel free to keep sharing ideas.

Anyone considers himself pro with K10Stat ? There are some settings I would appreciate help with.

Thanks,
February 15, 2010 8:02:49 AM

pkw4 said:
well if you get a voltage drop in the psu rail..,,, for example when your graphics card starts to kick in when playing a game, thats all it could take to make the pc lock solid as the little spike of a voltage change will cause instability if the core voltage is at bare minimum.
that 0.875v is the minimum to get the cpu to work not run efficiently, think of it like a 2-stroke engine, not enough oil it will seize solid when a load is put on it.


My pc doesn't start anymore after putting voltage of CPU at 1V, what can I do?
Processor: AMD phenom 2 X4 965 Black Edition 3,4Ghz
February 15, 2010 10:11:51 AM

If you can get to the bios, load defaults.

If not, unplug the computer from the electricity and remove the CMOS battery. Then, put it back. That will reset everything.
a b K Overclocking
February 15, 2010 11:11:29 PM

Also, when you try undervolting, only decrease it by 0.125 volts at a time and stress test it. I would start around 1.25-1.275V. Also do you use the C2(140W) or C3(125W) stepping?
a b K Overclocking
June 14, 2010 10:56:51 PM

If anyone is still looking into this matter, I was able to use the CnQ default voltages with a 300FSB/HF ref clock.

So with CoolnQuiet operational, I run 1200mhz with 0.975V, 3150ghz with 1.15V, 3750ghz with 1.25V, and finally 3900ghz with 1.47V.

I've also gone as low as 3333ghz with only 1.23V for the CPU voltage, in terms of undervolting without CnQ.

This was done on a MSI 790FX-GD70 mobo with a v1.12/1.C BIOS(latest official BIOS) and a Phenom II x4 955 C2.
February 6, 2012 8:57:18 PM

I have a Phenom II 955BE. It was running at 47 degrees idle at 1.4v. Reducing to 1.3v in BIOS (and doing nothing else) it is just as fast in WEI testing and stable but runs 8 degrees cooler.
!