CPU Temperature required for auto-shutdown

At what temperature do most motherboards/cpus power down to prevent damage?

And what determines this? Is it the bios, the motherboard, the cpu itself?

I have a cpu that stays on in the bios until about 105 C and then shuts down. I am not sure if this is correct? Maybe the sensors are wrong. I think 105 is a bit high. I guess 80-90 would be more reasonable for an auto shutdown.

Max CPU temp is entirely dependent on the model of CPU. The manufacturers make these values readily available on the spec sheets and white papers for each CPU. Most aftermarket motherboards have the ability to choose which temperature an overheat shutdown occurs at. Most vendor-supplied boards (from Dell, HP, whatever) have this feature locked at the recommended value for the CPU that ships with the computer.

Personally I consider 70C to be the red line cross, especially for AMD CPUs, which are said to be more vulnerable to overheat.

One thing is certain: 105C is absolutely too much.

105°C is about right. AMD processors have a THERMTRIP# signal that is asserted when the temperature goes about that high (it can change a little based upon process variations). Intel also has something like this. THERMTRIP# tells the motherboard to shutdown immediately to avoid a damaging thermal event.

There are also lower thermal event thresholds which the BIOS or thermal control subsystem would use to control fan speed, etc.. The lower one is typically called THERM# and alerts while heating up and the higher one is ALERT# which is usually the last event the software handles. THERMTRIP# fires at an even higher temperature and is hardware only.