Cooling
On e type of cooling is a heat sink. This is a block of metal with different segments inside it to spread the heat more evenly and make it so that the chip, e.g. the CPU, doesn't overheat and fry. The heat sink is usually secured with thermal paste that is used to firmly place the heat sink on top of the chip and so that the conduction is better between the chip and the heat sink.
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Having a fan in a PC is very important as the CPU can't go above 60 degrees so it will be too hot so it will just break. A fan is the cooling part of the PC that cools the system down so its nice and cool, so it doesn't overheat.
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Another type of cooling that is more expensive but better than having fans is called, water cooling, this is much more efficient so it uses water pipes that go all around the system to cool down each component so it doesn't overheat, but this would only be needed on bigger, more powerful and more expensive PC builds.