Yesterday I was compiling a Linux kernel on a Mac Mini that we have at work and it pretty much maxed out the fan to the point where I was seeing CPU throttle messages scrolling by on the console.

This got me thinking — wouldn’t it be cool to know how hot it got?

This is from a calibrated Agilent (I still don’t want to say Keysight) multimeter with a K-type thermocouple taped to the exhaust port of the Mac. Readings were taken every second.

This was two main parts: building the kernel then building the modules. The cool thing is you can clearly see both parts of the build process based on just the exhaust temperature.

Another interesting observation is the little bit of hysteresis on the temperature. What’s going on is the heat sink starts to get hot (sinking the heat) for a while. The fan, on the other hand is slaved to the CPU temperature. Once the heat sink is saturated the fan goes on higher. The CPU is still dumping heat, while the fins of the heat sink cool off a bit. This leads to the dips.

Why do this?

As GLaDOS famously said: “We do what we must because we can.”

Same thing.

Oh, max temp: 62.6 ºC / 144.7 ºF.