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 Post subject: underclocking laptop Core 2 Duo
 Post Posted: Mon Jan 03, 2011 8:09 am 
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Joined: Tue Jun 10, 2008 7:44 pm
Posts: 358
Location: Bellevue, WA, USA
Hi Scott,

I noticed that a friends laptop with a T5750 cpu runs at 1Ghz at idle (2Ghz max), wheras my P8600 runs at 800mhz at idle (2.4 max).

I was wondering if I could change the lower setting on the friends laptop to run at a lower clock speed, say more in line with mine, that would reduce the heat and power consumption also.

Just curious!
Thanks!
-Paul


Last edited by paulgj on Wed Jan 05, 2011 2:18 am, edited 1 time in total.

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 Post subject: Re: undercloking laptop Core 2 Duo
 Post Posted: Mon Jan 03, 2011 11:31 am 
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Joined: Sun Feb 04, 2007 11:44 am
Posts: 6115
Quote:
I was wondering if I could change the lower setting on the friends laptop to run at a lower clock speed, say more in line with mine, that would reduce the heat and power consumption also.

Unfortunately that is not possible. Processors with EIST (Enhanced Intel Speedstep Technology) have a HFM (High Frequency Mode) which varies according to the specific model, but multiple processors within a model range have the same LFM (Low Frequency Mode).

For example, T54xx through T58xx processors vary from 1.66 to 2.0GHz in HFM, but all run at the same 1.0GHz in LFM. However, the P8600 (Penryn core) is completely different from the T5750 (Merom core). The Penryn core introduced a new "SuperLFM", which drops the speed, voltage, and power consumption even further. For example, P7xxx through P8xxx processors vary from 2.0 to 2.8GHz in HFM, but all share a common 1.0GHz LFM and 0.8GHz SuperLFM.

Bottom line: The LFM and SuperLFM speeds are fixed and unchangable for a given model or family of CPUs. You can find more information on EIST here, and more information about the specifically supported HFM, LFM and SuperLFM speeds in the processor datasheets and specification updates.

Note that newer Nehalem microarchitecture based processors (i.e. Core i-Series) introduced a faster-than-HFM mode called Turbo Boost Technology that allows the processor to "opportunistically and automatically run faster than its rated operating frequency if it is operating below power, temperature, and current limits." This means that when running applications that use less than the full number of cores in the chip, the cores that are being used will automatically and dynamically overclock to increase performance. Scott.


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 Post subject: Re: underclocking laptop Core 2 Duo
 Post Posted: Mon Jan 03, 2011 11:12 pm 
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Joined: Tue Jun 10, 2008 7:44 pm
Posts: 358
Location: Bellevue, WA, USA
Thanks for that info Scott. I found this article about undervolting which seems like an alternate way to achieve the same result although I am leery of messing with the voltages:

http://www.clunk.org.uk/forums/guides/1 ... essor.html

Thanks!


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