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macrumors 68000
Original poster
Sep 12, 2007
Did some testing earlier to see what core temps/heatsink temps trigger the turboboost to clock down from 3.46 to 3.33ghz using Intel Burn Test (Linpack).

Now, this is the interesting bit:

Case A
Start from cold to windows, core temps reach 95C, starts throttling (3.46 to 3.33Ghz), SMC spins up fans, but the fans never get fast enough to allow the CPU to stay fixed at 3.46Ghz.

Case B
I fix the fan speeds in OS X to 1000RPM intake & exhaust fans and 2000RPM for the CPU fan. Restart into Windows (fan speeds are kept through a restart) and run IBT again.

This time, it starts throttling (3.46 to 3.33ghz) at 65C core temp! :confused:

Now, given I have never found a way to check actual CPU frequency in OS X, you can only really test in windows.

It is a small change from 3.46Ghz to 3.33Ghz but the SMC must be thinking that if the fans are spun up then clock speed should be reduced? :confused: Or it is hitting the 125W power limits, but why would it at a lower temperature? *shrug*

Could just be software errors but still seems weird to me. Anybody else want to test? I don't think this happened with my original W3520 but still.


macrumors member
Sep 4, 2011
Or it is hitting the 125W power limits, but why would it at a lower temperature? *shrug*.

You flashed the EFI of the 2010 as well onto your MacPro4,1 to turn it into a MacPro5,1 ?

Did the same thing. However - i find my mac pro to continously run at 3.46 GHz (although no IBT) instead of 3.33 ... turbo boost fequency for 6 cores is 3.46 .. so why is the processor a 3.33 then? this confused me

and for your question about temperature and wattage, wattage is pure volts x amps. if the fans keep the sink cool enough, it will throttle down due to high current even if the temp is below 90 or whatever Tjunction they use.

testing frequency in mac os is hard. HWmonitor (not the guy that makes temperature monitor, a different one) has one which is more for a hackintosh, but with a few fakesmc addons it might work? i found that luxmark reports cpu speed - but not sure if it will adjust for a turbo boost fequency.


macrumors G3
Jul 24, 2009
Op your processor isn't being throttled if it were it'll drop below it's 3.33 speed. You'll only see 3.46 in short bursts for single threaded computations.
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