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Geek Culture / What is the exact reason for which CPUs generate so much heat?

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Dark Java Dude 64
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Posted: 7th Jun 2012 14:14
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I have always wondered what the precise reason that very large scale integration ICs such as CPUs, GPUs, etc generate heat. Is it just the large amount of current passing through various parts of the IC as transistors transition between high and low logical values? I have also heard that any time current starts or stops flowing, heat is generated. My guess would be that when current stops flowing, the energy is dissipated as heat. Are the aforementioned reasons the cause for the heat or is it something else? Thanks in advance for any answers!

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Van B
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Posted: 7th Jun 2012 14:36
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The heat is caused by the electrons colliding with the ions that make up the conductive material... electrons convert their kinetic energy into heat when they collide.

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Dark Java Dude 64
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Posted: 7th Jun 2012 14:42
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So simply just the current flow?

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Nateholio
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Posted: 7th Jun 2012 15:33
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Van B has it.

Additionally, CPUs are made of semiconductors, which aren't exactly the best thing to be running electrons through. However, even excellent conductors like Cu, Au, & Ag will heat up if enough electrons are pushed through them.

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Dark Java Dude 64
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Posted: 7th Jun 2012 15:49
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I see! So then it would just be current flow during the high to low or low to high switches. Right?

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Nateholio
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Posted: 7th Jun 2012 15:54
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That's what causes a lot of heat. Switching states generates more heat than staying in a single state. However, the smaller components get the more heat they generate with the same amount of voltage.

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Jimpo
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Posted: 7th Jun 2012 16:07
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Electricity is made of electrons, and electrons are always randomly moving. The transistors on the CPU are so small, that the random movements can cause the electron to step out of the transistor, and be lost as heat.

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TheComet
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Posted: 7th Jun 2012 18:15
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Pretty much everything has been said.

I'll throw this into the mix : http://en.wikipedia.org/wiki/CPU_power_dissipation

You can calculate the maximum power P with this:

P = C * U^2 * f

C = capacitance
U = voltage
f = frequency

Not quite sure what they mean with capacitance though.

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Nateholio
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Posted: 7th Jun 2012 18:19
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Quote: "Not quite sure what they mean with capacitance though."


Everything has capacitance, which needs to be accounted for in some calculations.

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TheComet
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Posted: 7th Jun 2012 18:29
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Yes but WHAT capacitance? You mean I have to go ahead and add up every single capacitance in ever transistor? The entire capacitance of the CPU varies depending on what it's doing. Why is it no one can give me a straight answer about this.

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Dark Java Dude 64
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Posted: 8th Jun 2012 00:44
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Yah I'm thinking it must somehow be the capacitance of the gates on the transistors... Maybe it is an average capacitance over time?

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Sergey K
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Posted: 8th Jun 2012 00:59
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every place where there are electric, there is heat. learn for life!

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