散热器测试的价值有多少？谈温度监控

Hello from Canada,

When running a high stress program like Prime 95 Small FFTs, the core temperature is about 25C hotter than the temperature at the center of the IHS or heat spreader on top of the cores.  This is where Intel recommends that the Tcase temperature should be measured.  When you are using a large air cooler, the side or top of the cooler will not feel very hot to the touch even when the core temperature is very high.  It''s impossible to accurately judge the core temperature based on how hot the heatsink feels because the heatsink may only be a few degrees greater than body temperature.  It will feel warm but that''s about it.  The heat dissipates very rapidly with some of the big, efficient air coolers that are available these days.

There are a lot of problems with the sensors that Intel uses in all of their Core 2 based 45nm CPUs.  There are a lot of variables which makes it difficult to do a fair temperature comparison between two different CPUs.

The first problem is that Intel has never properly documented TJMax.  They released some information about TJMax last year at their IDF conferences but some of the information released does not seem very accurate at all.  They also didn''t include details like how much error is in their TJMax specification number.  With 45nm there seems to be as much as 10℃ of variation in TJMax and that''s from one core to the next on the same CPU.  Without trying to do some sort of calibration to minimize this amount of error, accurate temperature comparisons are difficult.

The next problem is slope error in these sensors.  The futher you get away from TJMax, the more these sensors will move at a rate either faster or slower than changes in the actual core temperature.  At idle, this can result in another plus or minus 10 degrees of error.  Intel has never documented the size of this error.

You can have two CPUs that have the exact same part number but one might read too low at idle while the other one reads too high.  An actual core temperature of 40℃ might be displayed on one CPU as 30C℃ and another CPU might show that as 50℃ even though the core temperature is exactly the same on both CPUs.  There are methods I''ve come up with to try and calibrate these sensors but very few users bother to do this.  Most temperature comparisons I read about are meaningless because of the amount of possible error.

The next problrem is sticking sensors at low temperatures.  It''s possible for a sensor to get stuck at 50℃ and it will keep reporting this number even as the actual core temperature gets cooler.  This can make users think that their CPU is running "hot" but it might just be more sensor problems.

What I found during testing was that if you had sensors that weren''t sticking and if you calibrated them then there isn''t a big difference in the core temperature at idle between a wide variety of Intel''s CPUs; Dual and Quad cores. 
At full load, if you have two 45nm dual Core CPUs and run them on the same motherboard, with the same heatsink and fan and at the same core voltage and at the same speed with the same load; there''s not a lot of difference in temperature either.

I think many users try to make temperature comparisons that are not very fair and don''t take in to consideration the significant problems these sensors have.  You have to do a lot of work to try and make a fair comparison.  Different users with different cases and air flow and room temperatures and 101 other things rarely equalize all of these factors and variables for a fair comparison.
I hope this makes some sense.  If you don''t understand something or don''t agree or need some more information then write back.

Here''s the latest version of RealTemp I''m working on:
http://www.fileden.com/files/2008/3/3/1794507/RealTempBeta.zip

As long as your computer is stable at full load then core temperatures aren''t too important.  I''ve learned to run Intel''s CPUs as cool as possible for maximum performance and not to worry too much about exact temperature numbers because the sensors are too inaccurate.