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 TCaseMax, How high is a safe max temp?

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gsan
post May 20 2007, 10:07 AM

Electrical RF Engineer
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This is a new type of program, which checks AMD64 CPUs for their maximum rated case temp or TCaseMax and reports the TDP which corresponds to the processor in question.
On most AMD processors TCaseMax and TDP values are constant, and depend on CPU type and model, but on the E Revision chips, both this values and the default voltage are variable.
These are the chips that have variable values:
Athlon64 (Venice, San Diego)
Athlon64 FX (San Diego)
Athlon64 X2 (Manchester, Toledo)
All Rev E Opterons and Dual Core Opterons
What this all means is this: On 90nm manufacturing process, the power leakage of transistors on individual processors differs greatly, this is why AMD implemented TCaseMax. Each CPU has a different TDP rating, here's how it works:
A program reads the TCaseMax value off the CPU, then depending on the processor (CPU type like A64, Opteron;CPU Rating like 3500+, 146) it finds the processor's Thermal Profile (If you download the "AMD Opteron(tm) Processor Power and Thermal Data Sheet" and look at pages 10-11 you'll see the different thermal profiles). When the thermal profile is determined, the program finds the TDP rating that corresponds to the CPU's TCaseMax value.
So in a few words, the higher the TCaseMax, the higher the TDP of a processor will be (the transistor leakage is higher), so the processor will run hotter. Several people have reported that the Opterons rated at 71C TCaseMax were pretty hot. On the other side these processors will be able to reach higher clock speeds.
That is why we see that on average processors with higher TCaseMax can usually reach higher CPU speeds when overclocked.
Every CPU type (A64, FX, X2, Opteron, DC Opteron) has a different thermal profile, that is why you see that on an FX a TCaseMax rating can be "only" 57C and it'll overclock way better than an A64 with a 57C TCaseMax rating. That is because at 57C TCaseMax, an FX has a TDP of 77W while the A64 has a TDP of 44W.

Right now we're working on getting a php page up where the user will be able to upload his CPU stats to the server and be able to see what other people could manage with the same chips, or look at other CPUs with different ratings and see what they're capable of.

We believe this will be a great way to be able to roughly predict the overclockability of a CPU even before overclocking.
We hope you find this software useful.
gsan
post May 20 2007, 01:00 PM

Electrical RF Engineer
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Senior Member
2,471 posts

Joined: Jan 2003

QUOTE(kmarc @ May 20 2007, 11:32 AM)
@gsan, thx for the info but I've read it before and roughly know what it is about.

What I'm asking is that how NEAR can we get to the TCaseMax in overclocking.

Like what gengstapo said, he's core temp goes above TCaseMax!!! Is that recommended? Or is there a low temp recommendation?

I guess in OC, everyone would say that the lower the temperature, the better it is for the CPU......
*
bro, as I told you before, the TCaseMax is not the measurement as what you meant by. if you really scare the proc will gone in one day later, then do not overclock. smile.gif

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