Sign in with
Sign up | Sign in

Assessing Voltage

Updated: Tuning Cool'n'Quiet: Maximize Power And Performance
By

Let's see the default voltage settings for the six processors and their respective p-states in K10Stat.

Athlon X2 7750

Athlon X2 7850

Athlon II X2 250

Phenom II X3 710

Phenom II X4 945

Phenom II X4 955

The Phenom II X3 710 is using the same core voltage below 1.9 GHz, regardless of clock rate. In addition, why does it need a boost in northbridge voltage at the lowest p-state? We suspect this is simply not needed, since the northbridge doesn't change clock rates (1.6 GHz).

Note: additional testing on an updated platform using both Socket AM2 and AM3 motherboards reveals that you don't have much room to undervolt the northbridge on an AM3 motherboard. In our discussion with AMD leading up to this story, the company stated that the values are chosen with good reason, and undergo a thorough testing process. We believe the settings were optimized for Socket AM3-based platform. With only core voltages with which to play, we saw a very small drop in idle power consumption (8W) via undervolting. That is in addition to a difference of 10 watts, which means power consumption on the AM3 platform is roughly the same as an undervolted AM2/AM2+ platform.

AMD is also quick to point out that running Socket AM3 processors on an AM2 motherboard (single power plane) is not officially supported. It is still possible of course, and we encountered no problems whatsoever during testing (even with forced Overdrive settings for the Phenom II X4 955 BE). However, that doesn't mean it's an optimal configuration. The power measurement tests we ran confirm this. All else being equal, you should see a Socket AM3 platform consume less power than an AM2/AM2+ platform with the same AM3 processor installed. In retrospect, AMD explicitly stated this when it first launched its Socket AM3 processors.

One final note about these voltages. You can see from the screen shots that the option for changing core and northbridge voltages is available with the Phenom II X4 945, but not for the Athlon X2 7750 or Phenom II X3 710. That's not due to differences in the processor, but rather the motherboard used. Core voltage selection in K10Stat was not available on the Biostar TA790GX 128M, but it was a viable option on the Gigabyte MA-790GP-DS4H. This relates back to the number of power planes implemented by the board vendor. The TA790GX 128M is not a dual power plane motherboard, so you can’t change the core and northbridge voltage independently of each other.

Display all 48 comments.
This thread is closed for comments
Top Comments
  • 13 Hide
    cyberkuberiah , November 16, 2009 7:00 AM
    On the behalf of all readers , Welcome , and so to say , Hi! , Arnawa Widagda :) 
  • 12 Hide
    DrgnRebrn , November 16, 2009 5:58 AM
    Nice article! I'm curious to know if the "e" CPUs can be affected in the same way, such as the Phenom II X3 705e. I have chosen this CPU for a HTPC build because of it's already low 65W TDP. Also, what are the effect to power usage when using ACC features & enabling dormant cores?
  • 12 Hide
    Anonymous , November 16, 2009 11:12 AM
    Very good article! Undervolting it's a great tweak to make and most of the people don't even know that it is possible as well as overvolting, getting a power efficient processor for no money! Thanks tom's for caring about this matter.
Other Comments
  • 12 Hide
    DrgnRebrn , November 16, 2009 5:58 AM
    Nice article! I'm curious to know if the "e" CPUs can be affected in the same way, such as the Phenom II X3 705e. I have chosen this CPU for a HTPC build because of it's already low 65W TDP. Also, what are the effect to power usage when using ACC features & enabling dormant cores?
  • 13 Hide
    cyberkuberiah , November 16, 2009 7:00 AM
    On the behalf of all readers , Welcome , and so to say , Hi! , Arnawa Widagda :) 
  • 3 Hide
    Inf3rnal , November 16, 2009 7:06 AM
    I'd like to see same article about Intel i5/i7 power setting tweaking.
  • 5 Hide
    razor512 , November 16, 2009 11:11 AM
    did any of these changes negatively effect performance?
  • 12 Hide
    Anonymous , November 16, 2009 11:12 AM
    Very good article! Undervolting it's a great tweak to make and most of the people don't even know that it is possible as well as overvolting, getting a power efficient processor for no money! Thanks tom's for caring about this matter.
  • 1 Hide
    nukemaster , November 16, 2009 11:18 AM
    My old A64 3200+ is about to get this treatment
  • -8 Hide
    autoimmune , November 16, 2009 11:36 AM
    Inf3rnalI'd like to see same article about Intel i5/i7 power setting tweaking.
    O my GOD i bet the writers at Toms Hardware had not thought of that, and are not currently in the process of writing that article!
  • -2 Hide
    whiz , November 16, 2009 12:12 PM
    Oops!
  • 0 Hide
    Anonymous , November 16, 2009 2:01 PM
    i love you guys. i have just the system that i am using as HTPC. i was wondering about ways to reduce the power usage as i dont use it for hardcore gaming or any other cpu intensive jobs. all i use it for watching blurays and tv and other movies and songs. i have an ASROCK 790gxh 128M mobo. and 1thlon x2 7750 kuma, that i bought from newegg for $59 (darn steal for the performance it gives. the machine has almost zero latency for any operation)
  • -2 Hide
    Jerky_san , November 16, 2009 2:19 PM
    Anyone know where to get k10stat?
  • 0 Hide
    cushgod , November 16, 2009 3:05 PM
    Google it Jerky
  • 0 Hide
    enzo matrix , November 16, 2009 3:25 PM
    Great article. I've been undervolting my Athlon 64 x2 in my laptop with K10stat for the past few months. The tx2500 models get hot. On load I went from a maximum of 90C to a maximum of 75-80C. Haha. no longer worried. Plus my fan doesn't go on maximum unless under full load anymore.
  • 1 Hide
    mende21 , November 16, 2009 3:31 PM
    It's great to see an in-depth article about k10stat. I discovered that program a couple of months ago and use it to underclock and overclock my 955. I hated disabling cool n quiet to overclock my processor and k10stat works great. I have it set to underclock to 400mhz at idle and overclock to 3.8ghz under load. After reading this, I think I can lower the voltages a little.
  • 2 Hide
    fsjis1 , November 16, 2009 3:34 PM
    It may be that AMD is making a purely dual core kuma and I am not aware of it, but I am fairly certain that the kuma series is actually a "phenom I" with two cores disabled, hence the L3 cache. I just did a google search and found people who have unlocked the extra cores on the athlon X2 7750 kuma. Nice article by the way I have been thinking about doing something like this to my PC's.
  • 9 Hide
    arnawa_widagda , November 16, 2009 4:50 PM
    First of all, thanks for all the comments and feedback.

    All Cool'n'Quiet 2.0 processors should work with K10Stat, so you should be able to use K10Stat with the Energy Efficient series.

    For those unfamiliar with K10Stat, here are some additional switches/options (insert these via the properties menu of your K10Stat shortcut).

    -lp:# - load profile# and write to MSR (activates a certain profile).
    -nw - Start K10stat with NoWindow (don't display window).
    -ClkCtrl:#(0-4) - Enable Clock Control (activates clock/core control).
    0:No Control
    1:UnGanged.
    2:Ganged (Load of Highest core).
    3:Ganged (Average load of all cores).
    4:Ganged (Load of Lowest core).
    -StayOnTray - puts K10Stat on the system tray. Use this option with “-nw” to keep K10Stat running. Very useful if you use sleep/hibernate.

    To those interested in Core i7/Core i5, a similar article is in the pipeline. We wanted to include the 32 nm refresh too, in addition to Core2Duo and Core2Quads, so we have to wait until (final) samples are out.

    About performance, performance differences and actual power consumption will be in the 2nd part - you'll see it soon. You might be (pleasantly) surprised.

    Thanks. Off to some more GPGPU testing.
  • -2 Hide
    Jerky_san , November 16, 2009 5:08 PM
    CushgodGoogle it Jerky


    People that say that tend to be fairly annoying.. Anyways I finally found a mediafire link.. all the geocities and rapid share links are dead..

    http://www.mediafire.com/?dywh3zhmk41
  • -5 Hide
    AMDnoob , November 16, 2009 10:33 PM
    can somebody tell me why my C'n'Q no longer functions? Go to my profile and look for the forum thread i started, it's all explained there.
  • 0 Hide
    nukemaster , November 17, 2009 12:45 AM
    Is there a K8 equivalent app?
  • -1 Hide
    Anonymous , November 17, 2009 12:54 AM
    I'm writing this on a 7750 (stepping 3) with a Foxconn A7GM-S motherboard, and CPU-Z reports 1.024V with Cool & Quiet on, and 1.312V at full speed. I'm not sure why you are observing different behavior.
  • -4 Hide
    wira020 , November 17, 2009 2:09 AM
    Nice article.. but it is a verrrrrrry lonnnnnnnnnnnng read.... hope you guys can simplify the article a bit... but nice research indeed... xD.. i'm just one of those lazy people that have a hard time reading thousands of words per page.. hehe...
Display more comments