Does On-Demand Clock Modulation (ODCM) conserve battery?

June 23, 2007 at 8:19 am 9 comments

Many low price laptop these days come with Intel Celeron M. Unlike its competitor, the AMD Mobile Sempron, Celeron M lacks dynamic frequency and voltage management. On processors like Mobile Sempron, Pentium M, Core Duo, and Core 2 Duo, the cpu drops frequency and voltage when there is less work load. So if nothing is going on, your cpu may drop from 1.8 Ghz to just 600 mhz and voltage may drop from 1.2v to 1.0v.

Celeron M in contrast runs at the same frequency and voltage all the time. This is why Celeron M typically have a shorter battery life than their mainstream cousins. Celeron M does have On-Demand Clock Modulation (ODCM). Can this be use to increase battery life?

How does ODCM work?

ODCM conjured up an image of a cpu dynamically changing the clock of the cpu depending on load. In fact, all ODCM does is force a processor to go into idle. Suppose you set the ODCM throttling to 75%. Your processor will work normally 75% of the time, and spend the other 25% slacking off. As a result, your cpu runs at the same clock speed and voltage, but runs slower because the cpu is forced to idle.

Does this actually save you power? Well, that depends on your usage. Suppose your cpu is running always at 100%, you are going to use a lot of power. Suppose you then set ODCM to throttle at 50%. 50% of the cycle will be idle, so you will use less power because the computer is at rest 50% of the time. However, the task will now take twice as long, this is not a good trade off.

If on the other hand, you’re going to do is type something in the computer, then your computer is probably idling most of the time waiting for you to press a key. In that case, power usage with ODCM and with ODCM is probably not all that different in both cases the computer is in idle most of the time. However, what if the forced idle uses less power than the natural idle state. Basically if you were to sit around and your computer goes into idle, does it use more power than if ODCM force the computer to idle? I decided to test this out.

The Test

The test platform consists of a Acer Aspire 3680 with a Celeron M 520 1.6 Ghz, 512 Mb RAM, and standard battery. I will run two trials.

  1. Normal Test – Laptop is turned on and left alone until the computer powers off.
  2. ODCM Test – Run RMClock and set it to throttle at 12.5%. Leave computer alone until the computer powers off. This causes the computer to go into force idle 87.5% of the time.

In both cases, we set the power manager to not turn off the monitor or hard disk. We also make sure nothing is schedule to run during the test. Wireless is turned off.

In both case, the computer powered off at about 2 hours. This mean that the forced idle uses the same amount of power as the normal idle. There was no power savings at all.


ODCM is not a useful tool for battery conservation. Most mobile processor conserve power by idling at a lower clock speed and voltage. ODCM is a poor substitute that attempts to force a processors to go into idle mode. However, since the force idle mode uses exactly the same power as the normal idle mode, you will not notice any power savings.


Entry filed under: CPU.

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9 Comments Add your own

  • 1. WebGyver  |  July 3, 2007 at 8:46 am


    I admire your tenacity and patience when you do tests like that. And I greatly appreciate your publishing your findings and insights with the rest of us.

    Awesome stuff! I’ll keep coming back for more.

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  • 2. Italo Loureiro  |  August 16, 2007 at 12:12 pm

    Awesome info on the Celeron processors. I got a Travelmate 240 running with Celeron 2.4Ghz Northwood core and I thought it sucked.. Now I know I have to set up my RMClock properly.

  • 3. Scott Ager  |  September 17, 2009 at 6:38 pm

    Good for you. I’ve been trying to interject a little physics and a little common sense to the gamers (twinkies) on the NBR undervolting thread. Not a whole lot of luck so far. The concept of a silicon circuit as just a switch doesn’t seem to relate. Sigh. Wade in. I could use a hand, ha ha.



  • 4. dykw  |  October 11, 2009 at 11:09 pm

    Then what’re the usage of clock modulation? People generally use clock modulation for what?

  • 5. dykw  |  October 11, 2009 at 11:09 pm


  • 6. PowerMaster  |  March 19, 2010 at 2:43 pm

    I’ve made a very similar test and had a device to measure the actual power consumption of my Pentium 4 (Northwood) based PC. When idle, it consumes about 75 Watts. With ODCM, no matter how I configured it, it still was 75 Watts.

    So, is ODCM completely useless? No! I found, that when under full CPU load, my PC consumers 125 Watts. Now, I configured ODCM (using RMClock) to use 75% of the clock in the ‘Power Saving’ Profile. Activating this profile, it fixes the ODCM to this setting. Now, under full load, I saw only 110 Watts instead of 125 Watts.

    Of course this means that under full load, with my setting of ODCM to 75%, the performance was not as good as it could have been. In other words, it conserves a bit power at the price of some performance.

  • 7. nick  |  July 22, 2012 at 6:40 pm

    ODCM is usefull for max temperature management. If your cpu is scorching itself, likely it is if left to stock settings, during media converting or similar tasks you can use odcm throttling to lower temperatures.

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