[Discuss] Cool Processing

[joe at polcari.com (Joe Polcari)]

And that?s why. Thanks.

From:  Drew Van Zandt <drew.vanzandt at gmail.com>
Date:  Friday, June 19, 2015 at 1:32 PM
To:  "joe at polcari.com" <joe at polcari.com>
Cc:  Richard Pieri <richard.pieri at gmail.com>, "discuss at blu.org"
<discuss at blu.org>
Subject:  Re: [Discuss] Cool Processing

You're assuming changing the voltage changes nothing else, if you try to
apply Ohm's law directly.  Many other things change when you change the
supply voltage of a semiconductor/PCB.

Among them:
Switching thresholds
Edge rates
Leakage currents
Capacitance of most of your capacitors

Drew Van Zandt
Artisan's Asylum Board of Directors
Firefly Arts Collective Board of Directors


On Fri, Jun 19, 2015 at 1:26 PM, Joe Polcari <joe at polcari.com> wrote:
> And ohm's law doesn't apply why?
> 
> Sent from my iPhone
> 
>> > On Jun 19, 2015, at 1:23 PM, Richard Pieri <richard.pieri at gmail.com> wrote:
>> >
>>> >> On 6/19/2015 11:02 AM, Steve Litt wrote:
>>> >> Today I have a 16GB RAM box, with dual core CPU (I wanted things to
>>> >> stay cool),
>> >
>> > I think I recently mentioned buying a new notebook. If I didn't, well I am
>> mentioning it now: a Mythlogic-branded Clevo P750ZM. It has a Core i7-4790K
>> processor. You read that right: a 15" notebook with a socketed Devil's Canyon
>> i7 desktop CPU. I think I have some grounds for saying that limiting yourself
>> to 2 cores is a poor way of managing heat.
>> >
>> > AMD and Intel processors draw substantially more power than they actually
>> need. Every processor is different and the minimum stable power varies so
>> they ship with the stock power draw set high enough that all processors in a
>> series will run stably. Excess power turns into waste heat. This is why my i7
>> quickly reaches 99C under load and throttles if I don't do something about >>
it.
>> >
>> > That something is called undervolting. As the name suggests it means
>> reducing the voltage that the processor draws. Since every processor is a
>> little different there is no single ideal undervolting setting. Finding the
>> ideal for a given processor requires some trial and error, same as
>> overclocking. A common starting point for Haswell i7 processors is -80mV
>> dynamic CPU voltage offset and -100mV processor cache voltage offset. My
>> 4790K barely reaches 80C with Intel XTU's stress test with these settings.
>> That's the same as the i7-4790S at 3.2GHz (what the notebook originally
>> shipped with) while running 20% faster at 4.0GHz. I figured that was good
>> enough and called it done.
>> >
>> > --
>> > Rich P.
>> > _______________________________________________
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>> > Discuss at blu.org
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