Measuring Temperatures with Thermal Probes and External Sensors - BIOS, Motherboard, and Software Readings
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We've learned how temperatures are measured on an architectural level. Nearly all of today's motherboards support voltage and temperature readings. This means that they have an IC (integrated circuitry) which basically steals (reads) the data out of the CPU and reports its measurements. Voltages are measured by other methods, but that's beyond the scope of this article.
The processor's core temperatures are read from using a diode installed just for us, the users, to report the measured values. Let's not get confused; this has nothing to do with throttling. This diode on the motherboard reads the temperature values which are made available through your computer's BIOS.
Actually, software readings are the same. So, you may use similar software utilities like Motherboard Monitor, ASUS Probe, SpeedFan, Everest, etc- these are basically the same BIOS readings. In almost every case, your motherboard will be auto-detected and then these reported values will be somewhat accurate. If your motherboard is not detected or supported by the monitoring software it will result in abnormal data interpretation so you will see inaccurate temperatures like 127C or a constant 0C. You'll sometimes even see some abstract ones like -150C or other similarities. You can usually guess when these are accurate or not.
You can reboot and enter your BIOS to check these temps. Then boot into your OS and check the monitoring software. You will be amazed by some of the huge differences. Then it becomes clear that the reported data is misrepresented. Another banal example would be a reading of '0' instead of a '1'.
Anyway, as a side note, you should always install the latest stable BIOS updates as they become available from the manufacturer's official web site. If the motherboard does not have the required chip to read data from your CPU's internal diode, then perhaps the motherboard itself has a thermal resistor/probe somewhere near the socket. Their disadvantage is that they are not close enough to get reliable temperatures, and they generally aren't calibrated. Even if they are, by adding a few degrees, it is assuming and this generalized reading could be way off in some cases.
Another important concept to understand is that even if everything is working correctly, you would like to assume everything is reported correctly. Unfortunately, it's not. BIOS readings are not always 100% accurate. Why? Because the on-die diode is some distance away from the actual heat source as we discussed in the first section. As a result, the measurements can't be absolutely correct. Thus, there is resistance between the diode and the other components inside the processor (resistors, transistors, and capacitors), silicon itself, and the diode too. This resistance is often approximately matched by manufacturers, but it can't be absolutely correct either.
Motherboard manufacturers have implemented features to get this information out of the diodes. Realizing that this information is not reliable, certain manufacturers, ABIT being the first if I recall correctly, have implemented changes in the BIOS to add a few degrees to temperatures read by the on-die thermal sensor. This caused a small war between ASUS and ABIT a few years ago in the enthusiasts community. It ended with ABIT getting the comment "ABIT adds a few degrees to measurements!" and ASUS getting "ASUS reads below the measurements!"
Most manufacturers nowadays are adding a few degrees. They're doing everything they can to match these readings as closely as possible. This is a fact. The thing is that manufacturers implement several different ways of reading and interpreting the temperatures. Most of the manufacturers now are adding a few degrees in plus.
Anyway, back in those days ASUS enthusiast users were bragging all over Internet forums that their cooling was better. It took quite a while for these differences to get noticed and it was discovered that it was just a mathematical equation. The I/O chip on the motherboard (Winbond, etc) reads the core temp data from the on-die diode and, with an equation, approximately calculates its value-which should be standard. I repeat, should be. You can see an example of a Winbond chip on a motherboard in the following photo:
Next: External thermal probes and how they can help >>
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