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CPU heat production

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Last response: in CPUs
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May 11, 2010 7:09:33 AM

Hello,
My friend, says that there are
two strategies for limiting the
heat production by a CPU. One
he loosely calls "duty cycle",
the other he calls "throttling".
"Duty cycle", he claims, limits
heat production by turning the
CPU on or off depending on
when instructions are or are
not available to be executed.
"Throttling", he says is a CPU
protection strategy depending
on a temperature sensor on the
CPU chip. I know about
"throttling" and agree with him.
But, I thought digital things
just draw more power when more
bits go through them. Never
heard of "duty cycle". What's
happening?
Sincerely,
Bill

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May 11, 2010 8:16:42 AM

I'm not sure that "duty cycle" is the right word in this context. The most common way CPU's save power is by reducing clock speed and voltage when they are not under load. (Intel Speedstep, AMD Cool n Quiet). This of course means less current and less heat. Intel's latest CPU's (Nehalem and later) also have a improved capability to cut off current to cores that are not in use, for example when running an single-thread application on a quad-core CPU.
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l
May 11, 2010 10:18:42 AM

Thanks for the quick reply Herr_Koos,
Is it OK to think of "power saving" as
the same as "throttling" then? Only
"power saving" uses the load value
to set clock and volts, whereas
"throttling" uses temperature to set
clock and volts? Am I wrong to think
that digital circuits just draw more
power when passing more bits?
Or is it this "power saving" strategy
that just makes it look like more
bits produce more heat? See
my dilemma? Does "throttling" have
Intel and AMD names?
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0
l
a b à CPUs
May 11, 2010 11:00:01 AM

Based on how you describe it, I think the "throttling" you refer to is a built-in safety mechanism that kicks in when the CPU exceeds a certain temperature, to prevent damage from overheating.
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l
!