CPU sensor readings - question

[mikeymikec]

Using CPUID HWMonitor, my board (ASUS M4A89GTD PRO USB3) is reporting the processor temperature as 38C.

Further down the page, the processor is reporting each core temp as 24C.

I'm guessing that the motherboard's CPU temp sensor is beneath the CPU or thereabouts, and that the CPU has its own temp sensors, but why would there be such a difference in readings?

If I start SpeedFan (which I've used with this board for years and I've checked its readings against the BIOS readings), and it agrees about the motherboard's CPU reading, however it has the CPU's own reading as a single figure of 26C (rather than each core reporting its temp as 24C).

 

[mfenn]

So if I'm understanding you correctly, a temperature probe in the motherboard hierarchy is reporting 38 C and a probe in the CPU hierarchy is reporting 24 C? If that's what you're saying then your supposition about the motherboard sensor being located beneath the CPU is very likely correct. The package substrate isn't terribly heat conductive, and there's not really any airflow in the inner pocket of the CPU socket, so that's a natural heat bubble.

The difference between those sensors is not altogether disconcerting. It means that your HSF is doing its job and conducting heat away from the processor die itself. Providing some airflow over the back of the motherboard will cool down that sensor, but at 38C, it's not really a cause for concern.

 

[Paperdoc]

My understanding is that each CPU has a temperature sensor built right into the chip inside, and sending out a signal via one of the CPU's pins to the mobo. I am not sure whether any CPU has two separate sensors for its dual cores - or more for multi core.

My inclination is to believe the temps displayed by the mobo maker's utility and also shown in BIOS Setup. The mobo maker knows exactly which CPU chips it accepts and how to read that CPU signal properly. Some third-part hardware monitoring utilities have difficulty with scaling the CPU signal and require a calibration setting specific to the mobo and CPU chip. I do not know whether CPUID has this requirement. I am a bit suspicious, however, if it claims to have a main Processor temp and two separate core temps to read, since I doubt the CPU and mobo have that many signals.

Normally, mobos have a few temp sensors: at least one as a general inside-the-case temp reading to use for case fan speed control, and maybe one or two in or very near the Northbridge and Southbridge chips (those being the mobo's own two chief heat generators).