[Discuss] Cool Processing

[Drew Van Zandt]

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 ZandtArtisan's Asylum Board of DirectorsFirefly 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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