Why do you need Core Temp?
Core Temp is a compact, light-weight, and yet efficient and powerful program to monitor processor temperature and other vital information of your computer’s “brain”. The top advantage of using Core Temp for the CPU temperature monitoring is its capability to display a temperature of each individual core of every processor in your system. You can see temperature fluctuations in real time with varying workloads.
All major processor manufacturers have implemented a "DTS" (Digital Thermal Sensor) in their products. The DTS provides more accurate and higher resolution temperature readings than conventional onboard thermal sensors. This feature is supported by all recent x86 processors by Intel, AMD and VIA are supported:
* Intel processors starting with the "Core" series all the way up to the newest Core i7, including all the derivatives.
* AMD processors starting with the first Athlon64 and Opteron processor series, all Phenom and AMD's new APU are supported.
* VIA processors starting with the C7 generation of CPUs, including all the derivatives based on the C7 architecture.
* All of the Nano based processors are supported as well.
The temperature readings are very accurate as the data is collected directly from a Digital Thermal Sensor (or DTS) which is located in each individual processing core*, near the hottest part. This sensor is digital, which means it doesn't rely on an external circuit located on the motherboard to report temperature, its value is stored in a special register in the processor so that software can access and read it. This eliminates any inaccuracies that can be introduced by external motherboard circuits and sensors.
How does it work?
Intel defines a certain Tjunction temperature for the processor. This value is usually in the range between 85°C and 105°C. In the later generation of processors, starting with Nehalem, the exact Tjunction Max value is available for software to read in an MSR (short for Model Specific Register).
A different MSR contains the temperature data. The data is represented as a Delta in °C between current temperature and Tjunction.
So the actual temperature is calculated like this 'Core Temp = Tjunction - Delta'
The size of the data field is 7 bits. This means a Delta of 0 - 127°C can be reported in theory. In fact the reported temperature can rarely go below 0°C and in some cases (Core 2 - 45nm series) temperatures below 30° or even 40°C are not reported.
AMD processors report the temperature via a special register in the CPU's northbridge. Core Temp reads the value from the register and uses a formula provided by AMD to calculate the current temperature.
The formula for the Athlon 64 series, early Opterons and Semprons (K8 architecture) is: 'Core Temp = Value - 49'.
For the newer generation of AMD processors like Phenom, Phenom II, newer Athlons, Semprons and Opterons (K10 architecture and up), and their derivatives, there is a different formula: 'CPU Temp* = Value / 8'.
*CPU Temp is because the Phenom\Opteron (K10) have only one sensor per package, meaning there is only one reading per processor.
VIA processors are capable of reporting the temperature of each core. The thermal sensor provides an absolute temperature value in Celsius, there is no need for any conversion or manipulation.
The Tjunction or TjMax temperature on VIA chips is usually between 70 and 90C. 90C for the mobile and low power versions and 70C is for the desktop variants.
Safe processor temperature
For processors with the "TjMax" value being shown in Core Temp it is usually considered best to keep the temperature 15-20C below that value when the processor is under full load.
For chips which don't provide a TjMax value, such as the AMD K8 family of chips, it's best to keep the temps under 70C full load.
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