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I have a quite basic question:

As far as I understand (correct me if I am wrong), we can summarize a computer by saying it is composed of wiring, transistors and some electronic components like capacitors for example.

The electric consumption of a computer mainly come from heat dissipation if I am not wrong.

Does this heat dissipation mainly comes from Joule effect in the wiring between the components, or from the components themselves (transistors) ?

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  1. A computer is usually defined by what it does rather than how it is built. Computers can (and have been) built from vacuum tubes, relays, discrete transistors, and integrated circuits (not a complete list). A simplified definition of a computer is that it is a device that takes inputs, operates on them in accordance with a set of instructions (which can be changed by the operator or even during operation) and then provides outputs which can be used to perform operations such as printing, running machinery, playing games, etc.
  2. All of the electrical energy consumed by a computer is turned into heat except for the relatively small amount that is contained in its outputs.
  3. The heat is partially from energy consumed in running current through the computer wiring but is primarily from the energy consumed by the transistors in the logic circuits that simultaneously have voltage across them and current through them. This energy is especially significant when the transistors change their states by switching between logic levels. This is why microprocessors dissipate more energy as their clock frequency increases.
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A desktop computer produces very little in the way of energy output relative to what it consumes. A bit of RF deliberately for Bluetooth and WiFi, a bit of current in Ethernet cables, some RF that is accidental, and some light. Just guessing perhaps a watt or less, if we draw the 'box' around all the peripherals that it is powering such as USB keyboards and such like. So yes, most of the power input ends up as heat.

Aside from the losses in the various power supplies, the chips themselves have a leakage current that is always there (in simple circuits, anyway) and a dynamic current that is caused by the charging and discharging of millions or billions of tiny capacitances within the chips. The faster the nodes change, the higher the voltage change, the larger the capacitances, and the more nodes are changing, the more current and thus the more power. Both of them act as loads on the power supply rails. Most of the power would be dissipated in the transistors (and for the dynamic power during the actual switching), not in on-chip or off-chip wiring. The dynamic power is proportional to the square of the supply voltage.

Each year, the chip features tend to get smaller (so less capacitance per node), the internal core supply voltage lower, and thus the power consumed per calculation tends to drop.

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The consumption in a computer is mostly due to transistor power consumption in the IC's. The display (whatever type) also consumes a lot of power. In a laptop, the LED backlight might be roughly 20% to 50% of the total. That is just kind of an estimate.

The joule heating in wires and such is not very significant compared to semiconductor power consumption.

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