Using my Core i7-860 with Turbo Boost @ 2.9Ghz I'm running Prime95 and getting temperatures of about 70'C on the Intel stock cooler... Are these "safe" temperatures for the CPU to run at?
Small FFT's? For how long? At what ambient temperature? Which processor temperature ... CPU or Core? What monitoring utility?
Here's what you need to know, especially if you intend to overclock once the socket 1156 brackets become widely available for the after-market coolers.
Temperatures and overclocking are all about specifications, so it's very important to be specific. If we're not, then the topic makes about as much sense as comparing apples-to-oranges thermal fruit salad in a blender! My objective is to assure that enthusiasts understand Intel's specifications, standards and test methods, so they can better decide how to apply and manage their overclocking options.
Core i and Core 2 processors have 2 different types of temperature sensors; a CPU case (not computer case) Thermal Diode centered under the Cores, and Digital Thermal Sensors located on each Core. The case Thermal Diode measures Tcase (Temperature case), which is CPU temperature, and the Digital Thermal Sensors measure Tjunction (Temperature junction), which is Core temperature. Since these sensors measure 2 distinct thermal levels, there is a 5c temperature difference between them, which is Tcase to Tjunction Gradient. Core i7’s / i5’s and Core 2 Quad’s have 1 Tcase and 4 Tjunction sensors, while Core 2 Duo's have 1 Tcase and 2 Tjunction sensors ...
... The monitoring utilities provided by motherboard manufacturers monitor CPU temperature, while some popular freeware utilities monitor Core temperatures ... Real Temp ... is recommended for users interested in monitoring Core temperatures only ... SpeedFan monitors Tcase (CPU temperature) andTjunction (Core temperature) ... "
The Thermal Specification shown in Intel's Processor Spec Finder is Tcase Max (CPU) not Tjunction (Core), which is a very common misconception among most enthusiasts. Since there's a 5c gradient between the CPU sensor and the Core sensors, (shown in the following Intel document) - http://arxiv.org/ftp/arxiv/papers/0709/0709.1861.pdf - just add 5c to the value shown in the Spec Finder to determine the corresponding Core temperature, which is 78c for all Core i7 8xx variants.
Intel's second and frequently misunderstood Thermal Specification, Tjunction Max, (100c for all Core i7 8xx variants) applies to overtemp protection such as Throttle and Shutdown, so you don't toast your transistors. As such, any i7 8xx Core temperatures which exceed 78c should be considered "overtemp". Further, when specifications are exceeded, then processor degradation becomes a concern, which is explained in the following AnandTech article - http://anandtech.com/cpuchipsets/intel/showdoc.aspx?i=3...
Prime95 Small FFT's is the Standard for processor thermal testing, because it's a steady-state 100% workload which yields steady-state temperatures, whereas Blend is a memory cyclic workload which yields fluctuating processor temperatures. Small FFT's will reach 97% thermal saturation within 7 to 8 minutes, so a 10 minute test is adequate. Thermal testing should be conducted as close as possible to 22c (72f) Standard ambient, with case covers removed, the computer clear of any desk enclosures, and all fans at 100% RPM to eliminate cooling variables, and to produce consistent and repeatable results for comparisons. If the Gradient between CPU temperature and "mean" (average) Core temperature is not ~ 5c, then BIOS is incorrectly coded. CPU temperature and Core temperatures can be individually calibrated in SpeedFan by following the Calibrations Section in the Temperature Guide.
OCCT and Burn Test (reminiscent of TAT) use LinPack, which shows thermal signatures that resemble the ups and downs of a bad day on the stock market, and cycle between light workloads, through test segments which spray all processor registers with all one's, (100% thermal load is equal to 115% workload), and can push an overclocked i7 8xx with HT enabled at Vcore Max 1.400, right on past Tcase Max to ring the Tjunction Max bell like a fire alarm!
Since there are very few applications or games that will spike, let alone sustain processor workloads beyond 70% to 85%, utilities which load all registers with all one's are not representative of real-world computing. While these utilities are certainly very useful for stability testing, they are inappropriate for thermal testing. The 3DMark benches are excellent for stability testing, as are applications for ripping and encoding.
To make sense of CPU temperature and Core temperature, compare them to a 4 cylinder car with 5 temperature guages; 4 of the guages are cyclinder head temperatures (closest to the heat source), and the 5th guage is the overall engine temperature, which is 5c lower than the other guages, and is the temperature guage with which we're all familiar. We know the red zone (hot) for the i7 8xx starts at 73c (Tcase Max) on the engine temp guage and 78c (Tjunction) on the cylinder head temp guages, but if we push the engine too hard and peg all the guages, (95c Tcase overtemp / 100c Tjunction Max) then the engine will shut down.
If you'd like to learn more about processor temperatures, then just click on the link in my signature.