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I recently found out that x86/x64 processors have a maximum temperature defined in their spec sheet. In the spec sheet the "maximum temperature" is referred to as the "Core Tjmax".

For example on an Intel Core i7 620M you can see the spec sheet here if you search for "Core Tjmax" you will see that this model has a maximum temperature of 105°C.

What happens to an x86/x64 computer when it's processor reaches "maximum temperature" or "Core Tjmax"?

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I can assure you my PC, I have an i7, turns off long before it reaches 105 degrees. –  Taylor Gibb Jan 8 '13 at 20:50

1 Answer 1

Short answer:

The CPU assert the PROCHOT pin and turns itself off.

It is up to the motherboard to act (or not) on that signal.

Longer answer

When the CPU gets hot (but has not yet reached emergency shutdown temperature) it will throttle itself. That means it will lower the multiplier and the voltage. As a result processing get slower but the CPU also generated less heat.

If that fails and temperature rises to then it will reach a point where the CPU asserts the PROCHOT pin and it does a full shutdown of the CPU.

More details can be found on intels site. Look for your specific CPU and select the correct datasheet. ( E.g. This one for some of their mobile CPU's)

AMDs x86/amd64's chips do something similar. (As do all modern CPUs)

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When the CPU signals with the PROCHOT, the motherboard is the one who cuts power to the entire machine? The PROCHOT signal and the motherboard shutdown happen outside of the OS' visibility? and thus prevent the OS from catching the signal and doing something with it? –  Trevor Boyd Smith Jan 8 '13 at 21:06
    
The motherboard is allowed to do that. If it does that or not is up to the designer. And PROCHOT can be set as an bidirectional signal (meaning the motherboard can also detect overheating and signal the CPU) rather than the default unidirectional signal (where the CPU asserts the signal to indicate that it will shutdown and where the rest of the MB may follow suit). –  Hennes Jan 8 '13 at 21:11
    
@TrevorBoydSmith: What would/could the OS do? –  Karan Jan 8 '13 at 23:08

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