[MacTUG] MacBook Pro owner notes on Different Max CPU voltages on 3 samples

[Marlon A. Griffith]

 From Accelerate Your Mac:

"I'm not an expert on the subject but i thought i'd share some things 
i've learned after experimenting with my three 2.16GHz MacBook Pro's. 
(apple replacements for various problems)

I noticed that my macbook's have all been set to different max core 
voltages (found this out from the windows side). This is definitely 
why my first MBP maxed out at 90 degrees (C) and used thermal 
throttle until the fans started. My latest MBP has a lower max core 
voltage and does not reach 90 even at the start of maxing the CPU's 
before fans kick in. I'm guessing that the varying core voltages is 
responsible for most of the maximum operating CPU temperature 
variation you hear about.

Interestingly, my latest MBP with lower core voltage (btw this does 
vary dynamically, but i'm referring to the max core voltage used when 
the cpu is running at 2.16GHz) does not overclock (the ATI X1600) 
quite as high as the previous one. I think this is to do with the 
core voltage being lower, but again i'm not familiar with intel 
hardware so i can't be sure. Anyway i've done extensive benchmarking 
and thermal throttle monitoring on both machines and found that with 
only modest GPU overclocks, the CPU thermal throttle will activate 
every few seconds since the system can't get rid of enough heat. For 
these tests super pi was used to max the CPU's with half life 2 
running windowed in the background. The thermal throttle is damn 
annoying, dropping the CPU's every few seconds depending on how high 
the GPU is overclocked. (Frame rate drops too!) Note that no throttle 
occurs under the same circumstances with GPU set to standard clock. 
Again, my MBP with lower core voltage ran cooler and was able to run 
with GPU overclocked higher before thermal throttling kicked in. 
(Can't remember the numbers, could find out for you though)

It sucks that some people have MBP's running at higher core voltages 
where throttling kicks in often; they probably dont even realise it, 
but you can check for yourself using either Coreduotemp (requires 
speedit kernel extension) or booting into windows and downloading a 
system utility monitor. Certainly i now understand why some people 
complain of having very hot MBP's whilst others don't.... I think 
that the later MBP's probably have lower core voltages, although i 
can't really be sure with a sample of only 3.

The higher core voltage MBP (ATI X1600) is stable around 480/550 
whilst the lower core voltage one is only stable at 460/535.
As i said, if you are playing a game that maxes the CPU AND the GPU 
at them same time you wont see much benefit at all from OC'ing as the 
thermal throttle kicks in heavily. The system just cant handle the 
heat.

When playing half life 2 at max GPU overclock on my lower core 
voltage MBP thermal throttle doesnt activate. It does on the other 
MBP, and explains the randomly jumping frame rate i used to see. 
Other games (Far Cry) make thermal throttle activate on both and 
hence you dont see much benefit from OC'ing. Its made me want to get 
a laptop cooler pad with fans. If i could just keep the temps down 
slightly i'd be able to benefit from a big overclock which really 
helps fps.

(Just for the record I asked if his other MacBook Pro's had the SMC 
firmware update applied as the Speedit kernel extension developers 
mentioned that update changed CPU voltages (among other things).-Mike)
yes i don't recall the voltage being different before the SMC. i use 
rightmark utility tool (in Windows) to view these settings, it gives 
current voltage and multiplier settings as well as the max settings 
etc.
Anyone with an intel mac could boot into windows and use this program 
to view the chip settings, it even lets u turn off thermal throttle 
and other things that i don't understand!

(I also asked if he remembered the actual different max voltages 
seen. (And not sure how much common variation there would be in max 
voltages from sample to sample)-Mike)
I could be wrong but the max voltage doesnt appear to have changed, 
it is still 1.250v at 2.16GHZ. This MBP runs at 78degrees C maxed out.
The other MBP runs at approx 84 C when maxed, and has a core voltage 
of 1.263v (from memory). Its not much of a difference but it is 
noticeable in temperature, and the amount of thermal throttling used. 
I used to load up dnetc on the hotter machine, throttling would kick 
in noticeable for as long as it took the fans to come on. The newer 
machine never throttles in OSX, i've only been able to get it to do 
that in windows with GPU OC.
kind regards
Ant"
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