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Phenom X4 955 And Conclusion

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

Phenom II X4 955 BE

Clock
Core and Northbridge Voltage
Idle
Load
2.4 GHz
0.900V
72 watts
96 watts
2.5 GHz
0.925V
74 watts99 watts
2.9 GHz
1.025V
79 watts113 watts
3 GHz1.075V
83 watts120 watts


After looking at the data above, it’s clear why AMD chooses to run its most energy-efficiency CPUs below 2.5 GHz. At those clock ratess, the Phenom II X4 955 needs only 1.0V (less, actually) and only consume up to 100 watts at load. Just to put that number into perspective, we saw the same level of power consumption from the Athlon II X2 250 at 3 GHz. With AMD’s 45nm process, you can either have two cores running at 3 GHz or four cores at 2.5 GHz with a 6MB L3 cache. Not bad at all.

The optimal combination of clock rate, voltage, and power consumption is almost the same as the Phenom II X4 945, which is 3 GHz. After that point, power consumption scales very quickly, just like it did with the Phenom II X4 945.

We were able to reach 3.6 GHz at 1.325V, which we were unable to do with the Phenom II X4 945. If you look back at the Athlon II X2 250, you’ll see we also had to apply the same voltage to get 3.625 GHz. The power consumption at that point was very high (188 watts), but that’s really only around 11 watts more than the Phenom II X4 945 at 3.5 GHz. Come to think of it, that’s only 14 watts less than running the Phenom II X4 955 at 3.2 GHz under load without power management at its default settings. You can probably get away with 3.4 GHz if you want push a little bit further.

A Tale of Three Motherboards

In the middle of the article, we mentioned some of the power/performance characteristics we observed during testing with these processors. Most of this variation is due to the motherboard used. Afterward, we also saw some differences in consumption. We were curious to see just how much a difference there can be. So, we installed the Athlon II X2 250 on all three platforms and ran some additional tests. Here’s what we saw.

At idle, the two Gigabyte boards practically offer the same level of power consumption. The Biostar TA790GX 128M is the platform that really stands out. At load, the Gigabyte MA790GP-UD4H was able to save a little bit of power, lowering its system power consumption to just about four watts higher than the TA790GX 128M. This is why we said the Athlon II X2 250 is more energy efficient than the Athlon X2 7750. With the right motherboard, it offers the lowest power consumption of all the processors tested here today.

The power consumption differences between these three boards may well be related to their respective HT voltage. The Biostar’s HT voltage is 1.25V, while the two Gigabyte boards employ 1.9V. Those familiar with HT voltages understand that higher settings might help achieve more aggressive overclocks. This is why we did not need voltage adjustments when we increased the HyperTransport clock on the MA790GP-DS4H. To achieve the same clock rate on the Biostar board, we generally had to use slightly higher core/nortbridge voltage settings. Power consumption is similar when the processor is fully loaded, but as you can see, it is different when idle.

Despite its shortcomings, the Biostar TA790GX is the board that offers very low consumption when paired with the right processor (like AMD's Athlon II X2 250). Hopefully, in the weeks to come, we'll have the opportunity to test more boards so we can see which one offers comparable power consumption without the caveats we’ve seen here. We found the Biostar TA790GX to be a good example of what you can achieve with AM3-class processors.

With both AM3-based CPUs, the default voltage are high enough to give us ample enough headroom for a roughly 400 to 500 MHz overclock. This is likely an effort to maintain stability across many thousands of CPU die, which, as we all know, vary from one to another. These settings are quite optimal for general usage when you match modern CPU to Socket AM3 motherboard. But that does mean the AM3 CPU/AM2+ motherboard combo leaves some room to squeeze out even better efficiency results, particularly for enthusiasts who know how to tune their machines.

By dropping the voltages to a bare minimum for each p-state, we were able to keep our system stable, dropping 20 to 25 watts of power consumption in the process. That's quite significant, since the test system's power footprint is between 100 to 200 watts total, depending on the processor used.

Of course, we have to admit the savings we got from undervolting the AM3 CPU/AM3 motherboard combo is small (typically under 10 watts). Is that worth the effort of tweaking your settings and testing for hours to gauge stability? The answer is up to you. If it isn't, you always have the option of buying one of AMD's energy-efficient low voltage models and paying upfront for power savings. This is, after all, an overclocking experiment and experience, tailored to the users who like to push the envelope just a little bit further than most.

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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
    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.
  • 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?
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...
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