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I installed a sensor reporting utility on my Ubuntu machine (a desktop machine) and it reports drastically different temperatures for the ACPI CPU reading and the ISA Core 0/Core 1 reading.

The ACPI says the CPU temperature is 31.5 C, but the ISA adapter reports the Core 0 is 55.0 C and Core 1 is 56.0 C.

Why do the "CPU" and "Core" temperatures differ? Are these sensors in different locations on the motherboard?

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Close voter(s): This is a question about ACPI in Ubuntu and how results are reported. While it happens to have an answer that explains it in terms of hardware, this probably should be considered to fall within the scope of our site. –  Eliah Kagan Mar 8 '13 at 5:47

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AMD Temp Information and Guide

We've had a few great threads recently where members contacted AMD and asked what temps they should be looking at, what the max temp was on, and what programs should be used and why. But this information is still scattered and not well defined in one place. It also doesn't quite explain when you should be looking at certain temps. Well I've made it my mission to insure that people are reading the right temps and have been trying my best to give all the information each time I respond without sounding like a broken record. So I decided to write this information thread and little guide to help you out there.

What is "Core Temp" ?

"Core Temp" is what AMD refers to as "TCTL" and is a non-physical temperature on an arbitrary scale measured in degrees. It does not represent an actual physical temperature like die or case temperature.

What is "CPU Temp" ?

"CPU Temp" is read by a sensor in the socket of the motherboard. It is a physical temperature and therefore will be effected by ambient temps inside the case.

Why should I use "Core Temp" and when?

AMD designed this equation to accurately read peak (45C+) and load temps. It has an equational offset to determine said temps which equalizes at 45C. Since it's designed for peak temps and is a non-physical temperature it cannot read idle temps or account for ambient temps correctly.

So what is "CPU Temp" good for then?

At peak temps this value is typically 7-10C higher (depending on motherboard) than the actual temp due to it being a physical sensor. At idle it's a little more accurate, but still not dead on, and besides idle temps do not matter near as much as load temps do.

AMD says my chip has a [INSERT SPEC] Celsius limit, what value is this referring to? This limit seems kind of low, why?

This is referring to "Core Temp" of course.

So for example Phenom IIs have a recommended 62C "Core Temp" limit while not exceeding 60C for extended periods.

It has long been argued that the recommended limit is merely a larger safety net. There is a thermal shutdown in the chip at 90C and the silicone is rated for 97C+, so it seems plausable that we could indeed go higher, but this guide (and most in general) will simply nod and point you to the recommended limit for your chip.

What programs read "Core Temp" ?

AMD recommends the Core Temp program and AMD Overdrive for this reason.

The core section of HWMonitor also reads this value, but be careful as it also shows CPU Temp.

From http://www.overclock.net/t/1128821/amd-temp-information-and-guide

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