Originally Posted by Catscratch
I always wondered it thou how CPU knows where to throttle down or shut off when there's an offset ? So cpu circuit has this offset correct then ? Why would amd not disclose this and keep saying "use core temp" to watch temps.
The CPU defines the offset. The internal temperature sensor is easily accurate to better than a degree C. The offset depends on the process (maybe even batch or bin???) and is programmed into the CPU unless they do it on an analog basis which they probably don't. So there's probably a simple 8-bit adder that subtracts 20-odd degrees from the A-D converted thermal diode reading. In their testing they probably have a way to read the real temperature.
Throttling starts on my 8150 at Tctl=73 AFAICT - that's when AOD starts to show smaller clock values than nominal (4500 on my box.) Note that the CPU has no direct access to the thermal monitoring that the motherboard does - the chip temperature is all it knows.
The offset is kept secret because a) Intel does it too and b) because back in the days when silicon manufacturing processes were black magic you didn't want to disclose anything.
It doesn't make sense anyway - if someone wants to know what real temperature a CPU runs at all they have to do is decap a die and put a thermocouple on it. Run the chip at various temperatures and you get an accurate mapping between core temp readout and physical temperature.
In AMD's case there might be a legacy reason too - not sure: They could have had a 70C maximum die temperature at some point in the past and decided to adjust the reading so that software doesn't have to change. That makes a lot of sense to me - I only have to look at my core temp readings and know that "70" (*not* C) is the limit - who cares what physical temperature the chip runs at? I don't. For heat flow and cooling purposes you use the maximum CPU case temperature which is in the data sheets too - typically slightly above 60C - that's your motherboard reading. If you know the case and the die temperature you can calculate the thermal resistance between case and chip - maybe that's a manufacturing parameter they want to keep secret.