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  1. #1
    AF-hwbot-team Avatar von OCool
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    Standard CPU Power Consumption - Intel Pentium D "Presler" C1

    I've recently taken some measurements from my Pentium D 915. Unfortunately I didn't have enough time to write an article about it, so I've got only the results for you with some short annotations in bad English.

    Test Setup:
    Intel Pentium D 915 (2,8 GHz) VID=1,25V, C1 Stepping
    GigaByte P35 DS4 with 6 phase CPU voltage regulator (Intersil ISL6317)
    1 GB Cellshock D9GMH
    Matrox Millenium
    be quiet! E5 450W

    Voltcraft VC920 (Vcore measurement)
    Allegro ACS712 Current Sensor (+12V CPU supply current measurement)


    The ACS712 is not suitable to measure the real CPU supply current with values over 100 ampere. For this purpose a current clamp would be needed, to which I haven't got access at the moment. Thus I measured the current in the +12V supply line of the CPU VRM. The measured power consumption includes the CPU power consumption and the power loss in the voltage regulator.

    Voltage regulators used for the CPU power supply have a typical efficiency at medium load of approx. 80% but up to 90%. The most important fact at this point is that VRM efficiency changes heavily with the CPU supply/VRM output current.
    This graph by IR shows some efficiency curves of different VRMs.

    This graph makes also clear, that a higher phase count mustn't be better for efficiency. A lower phase count has less switching losses at light load, while a higher phase count has lower conduction losses at high load. Please keep this exemplary efficiency curves in mind!
    Also the ratio between input and output voltage of a step down voltage regulator has an impact on its efficiency. The voltage on the 12V supply line can be considered as stable.

    The comparably low efficiency of the VRM at low load can also be shown by these two measurements:

    (1 core disabled in boot.ini, I hope it was really shut off!)



    Real Vcore vs. Bios-Set Vcore (Drop & Droop) vs. Power Consumption at fixed frequency


    Load was always tested with Prime95 large FFT setting.
    Voltages are rounded to 3 decimal places


    Real Vcore vs. Bios-Set Vcore (Drop & Droop) vs. Frequency vs. Power Consumption with fixed CPU supply voltage




    Vdroop vs. CPU supply current

    For everyone interested in Vdroop i recommend reading the Intel VRD 11 Specifications.


    I've done further testing with different multipliers, frequencies and voltages, but I don't think it's necessary to show them, until you are really interested in them...


    I also measured the impact of CPU temperature on the CPU power consumption.
    I'm sorry for not measuring the temperature directly at the CPU, but only using SpeedFan, which shows a temperature of about 10-15°C under the real value...
    This measurement should be repeated with an Intel "Core" CPU with an accurate and internal temperature sensor with a fast response.


    The results at 2016 MHz with 1,1V set in BIOS, idle and load:

    Also here, a voltage droop is clearly visible.




    The results at 2016 MHz with 1,4V set in BIOS, idle and load:




    Similar results at 3024 MHz and higher voltages:







    These curves should be similar in the negative temperature range until the so called "cold bug" is reached. If somebody is interested I could run some tests with my phase change cooler down to ca. -40°C.



    Always keep your CPUs cool, undervolted and reasonably overclocked ;-)

    OCool
    Geändert von OCool (27.08.2009 um 11:06 Uhr)
    [hwbot]13355[/hwbot]
    THE BIGGEST ROOM IN THE WORLD IS THE ROOM FOR IMPROVEMENT

  2. #2
    AF-hwbot-team Avatar von aperacer
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    I can see this was a lot of work and you done it well

    Asus P2B Kill Counter: 2||Asus P2B-F Kill Counter: 2

  3. #3
    Avatar von Yidaki
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    14.06.2007
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    Great work!

  4. #4
    AF-hwbot-team Avatar von OCool
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    Thanks guys!

    Comparison of stock settings (2,8GHz @ 1,25V), an underclock, a slight overclock and a "reasonable overclock" in power consumption at lowest possible voltage.


    I measure CPU+VRM, so you can take away about 10% from the 84,4 at stock settings to get a realistic CPU-only power consumption - the TDP is 95W btw.
    [hwbot]13355[/hwbot]
    THE BIGGEST ROOM IN THE WORLD IS THE ROOM FOR IMPROVEMENT

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