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wbmw

12/01/05 3:51 AM

#66914 RE: oc detective #66908

OC, Alan, you're both wrong.

All the tables do is perform a little math for you. Take the column row, subtract the ambient temperature, and then divide the result by the thermal resistance, and you'll get the value in the resulting column.

For example, the first result from profile A, at the row marked 49C degrees:

49 - 42 = 7
7 / 0.34C/W = 20.6 W

All this says is that if you are using the recommended thermal solution with total Tcase to ambient thermal resistance of 0.34C/W, and your product is giving off 49C degrees of heat (7C degrees over ambient), then you can effectively dissipate up to 20.6W of processor power before your processor temperature will begin to rise. It DOES NOT SAY that Opteron will dissipate this much if the core temperature reaches that high. In fact, depending on the application and what kind of code is run, and how much idle time occurs, the processor wattage will exceed this, and the processor temperature will rise.

The graph is helpful to determine how hot your system is going to get, given the thermal resistance of the cooling solution. So let's say you are using thermal profile B (most likely, dual core Opteron) with the system built to recommended thermal resistance of 0.27C/W. Now, you can look up on the table how hot the processor will be if it's dissipating, say, 70W of power. According to Table 9, it will be ~61C degrees (assuming 42C degrees ambient), or more accurately, simply 19C degrees over ambient.
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alan81

12/01/05 11:58 AM

#66947 RE: oc detective #66908

One more try at thermal wording...
This is what I think you are saying... correct me if I am wrong.
You are saying that if you look up the case temperature in table 9 you can find the TDP of the CPU?
This is not strictly true. For this to be true, you also have to have an ambient temperature of 42C and a heat sink/fan combo that gives you the thermal resistance stated for that column. For instance, assume with a part specified for thermal profile A, which has a thermal resistance of .34 C/W.
We then go in and measure the case temperature and find that it is 51C. We look at 51C in table 9 and find TDP is 26.5W. Does this mean the CPU is dissipating 26.5W? No it does not. IFF we really have a .34C/w thermal solution and the ambient is 42C then we are dissipating 26.5W. However, if the ambient is 25C then we are really dissipating:
power=(Tcase-tambient)/thermal resistance
power=(51-25)/.34 = 106W!
Table 9 does NOT give the characteristics of the opteron CPU, but rather the characteristics of the thermal solution.
--Alan