Accurate CPU Temp?

All of you need to chill out and relax.

@OP:

There are often two separate thermal measurement reference points on most motherboards. Enthusiast motherboards often have more.

The first reference point called the Thermal Junction, often abbreviated TJ. This is the temperature at the surface of the CPU die as it mates with the metal heat spreader (which is itself connected to the heatsink). This value is not measured directly, rather it is computed from a calibrated value set at the factory using a thermocouple, and a digital thermal sensor located on each core and below the main die. The value of the thermal sensor is subtracted from the calibrated value to yield an index value. The index value is then put through a lookup table stored in the system firmware to yield a corresponding temperature. The lookup tables may change with major and minor CPU revisions, so firmware updates are often needed to fix what may appear to be a wonky sensor value, such as an idle temperature that is below ambient.

The second reference point is a thermometer that is installed by the motherboard manufacturer. This thermometer is often located inside the CPU socket or very near to it. These devices are much larger than the digital thermal sensors located within the CPU, and are much more accurate as a result. However, they are farther away from the heat generating components, and as a result will always be cooler than the temperature measured at the thermal junction. This value should be pretty close to TCase, which is the temperature measured at the top of the integrated heat spreader.

CPU throttling and thermal protection is always performed relative to the TJ. TJMax is the temperature at which the CPU will enter a throttle state in order to bring temperature back under control. If TJMax is exceeded too far (such as may occur in the event of a failed cooling apparatus), the CPU will power down completely to prevent damage. Damage will not be incurred by hitting TJMax periodically, but the lifespan of the CPU will be reduced if it is chronically close to TJMax over a long period of time. It may reduce it from 10 years to 7 years for example; most people will replace theirs long before it dies from heat.

The TJMax for Intel CPUs is around 90 degrees centigrade.

The formula for this is simple: under a constant electric force, electromigration occurs at a rate proportional to temperature. Part of the semiconductor manufacturing process involves baking the IC at hundreds of degrees (over 600 degrees centigrade) for hours on end in order to activate dopants that have been implanted in the substrate. Semiconductors can take the heat, but the metallic interconnects that join the transistors together will decay at a greater rate when an electric force is applied at high temperatures. Eventually they will decay to the point where the supply voltage needs to be increased in order to maintain stability, and eventually they will fail completely.

Maintaining load temperatures near TJMax may also cause undue stress on the surrounding components that are not quite as heat tolerant. Thermally induced stresses can damage a poorly manufactured PCB as well as change the characteristics of certain electrical components such as electrolytic capacitors which are used to provide steady voltage to the CPU.

So, running a CPU at high temperature is fine as long as one is aware of the consequences and has equipment that is suitable for doing so. Both AMD and NVidia have designed their most recent families of GPUs to run at 95 degrees and 80 degrees respectively; this necessitated making adjustments to the design of the PCB and cooling apparatus to accommodate. These temperature values are used as performance targets, not upper bounds.

Now, behave!