I’m confused. I did some research online, and learned that cpu’s can essentially double has a hotplate, because 99-100% of electricity consumed is turned into heat. how? doesn’t the cpu use energy to make calcuations and render things? I’m real confused.
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The entire CPU is simply one and off switches. But billions of them.
If you look at it simply, all you are doing is putting electricity into a block of silicon and plastic and you get out electricity, so it is basically just routing electricity around, so it’s basically a resistive heater.
A light bulb could be a CPU too if you think about it. It can output something based on input. The input is you flipping a switch to either on or off and the output is light or no light. You can also bake cookies with the heat of a light bulb. Because it does both. It “calculates” some logic state for you (is the switch on?) but it also follows the laws of physics and produces resistive heat and light.
Now rewire your light switch so that when the switch is in the on position, the light turns off. Now you have a different sort of logic. Light is one when switch is off. Now add another switch in series with that … the light is on if both switches are on, but is off otherwise, you now have an “And gate”. Put two switches in parrallel to the light bulb. Now you haven “OR gate”. Cool! Now take 100 million of these and you have a computer. It will compute stuff, but also generate heat.
Your computer doesn’t use energy to do calculations, it uses negative entropy. It takes a highly ordered (low entropy) form of energy (electricity) and turns it into the most unordered form of energy possible (heat).
It converts low entropy into computation, and in the process it disperses the electrical energy as heat.
It’s like powering a water wheel with a river. You take water that’s upstream and it goes through the wheel and finally it continues through the river and ends up in the lake. 100% of the water ends up in the lake (this represents the 100% of energy that got transformed into heat), and the wheel didn’t consume water at all in it’s operation.
All energy turns to heat in the end. The CPU is just doing it in a more direct way than others. In fact just about the only thing that energy does and the way that we define energy is that it does work and generates heat.
When you use wood to create heat or light, you use it up and it becomes ash.
This is true of all fuel. The ash may be solid, or smoke, or a gas like CO2, but to use the fuel, you have to turn it into ash.
Heat, specifically heat that is dissipated into the world, is the ash of energy. When you use energy to do anything, you generate heat, and that heat is always spread out into the world. When you have more heat in one place than another, you can use this heat to make energy, but doing so spreads it out and thus uses it up.
When you use energy to do work, the result always is heat, and if you start with heat you always make more and the final heat is always more dissipated than what you started with.
Or, dissipated heat is ash.
Your brain does the same thing. You actually need the blood flowing not just for oxygen, but also to remove heat. Around 12 watts.
And so does the rest of your body. Heart, intestines, everything. And your cells produce heat as part of your normal processes. Which is why we are warm.
Calculations themselves don’t have any mass or energy. They are just intangible information that we humans find valuable. If you channel electricity into a wafer of silicon all that energy goes through the microscopic circuits opening and closing millions of transistors… and just stays inside. All the “work” of the CPU ends up as heat energy that we have to cool off to keep the CPU from melting. All the renders and calculations are a useful byproduct of heating the chip in a really complicated way.
The energy that goes into doing calculations must end up *somewhere*. Conservation of energy doesn’t stop when you use the energy to do calculations, or do anything else for that matter. Either the energy that you use to do useful things is stored somewhere where it can do more useful things, e.g. in a battery or a compressed spring or a fidget spinner, or it gets wasted as heat and can’t be used usefully anymore.
It just so happens that we don’t have the means to usefully store the energy that goes into performing calculations anywhere. Moreover, the fact standard CPUs are *irreversible* computational devices means that there is a fundamental minimum amount of energy lost in performing those calculations. However, this is a small fraction of the overall energy that gets wasted as heat in modern processors.
I look at it the same way you would look at an air conditioner. All it is doing is moving heat- by the mechanism of evaporation and condensation. The energy used by the air conditioner is purely utilitarian work; its job isn’t to create heat, but rather it’s what’s expelled as the device operates.
Similarly, a cpu MOVES data- which happens to be in the form of electricity- by the same concept. It consumes energy by manipulating those electrical charges inside the computer. The fact that those electrical charges are the same kind of energy as what powers the CPU is incidental.
The calculations don’t consume energy, they just move the energy around from one place to the other. Storing the result takes energy, too. You’re creating heat in every part of the process, not just the middle.
The electricity stays in the system *until* it radiates away as heat.
When water passes through a waterwheel, you get all the water coming out at the end.
When energy passes through a CPU, you get all the energy coming out at the end. The CPU makes all the energy into heat, because it is easy for electricity moving through wires to become heat, and not so easy to make it into other forms of energy.
Without electricity turning into heat, you cannot calculate. So indeed, your CPU uses energy to calculate, but the way it uses the energy is turning it from one form into another. Everything that “uses” energy turns it from one form into another, frequently as waste heat.
Instead of “using” energy, think of it as “transforming” energy. It is more valuable to have orderly energy than unorderly energy. Everything moving in one direction is useful. Everything moving uniformly randomly is heat: hard to make use of it. Once you make use of orderly energy, it becomes unorderly.
(Something something entropy, is not really ELI5 anymore)
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