[RC5] RC5 on laptops & CPU temperature

Per Hallström phand03 at student.vxu.se
Sun Nov 7 06:34:27 EST 2004


On Nov 6, 2004, at 23:54, SideWinder wrote:
>
>> That said, people do buy stands (or piles of books) to levitate their 
>> iBooks. I'm not sure how much this helps (probably quite a lot, since 
>> I'm quite sure the cooling fan is either on or off, and when it's 
>> off, the heat has to find other ways to get out).
>
> Again, this is probably something specific to iBook (and a few very 
> cheap PC laptop models I've encountered). Usually there is stepless 
> adjustment of the fan voltage (between 3-5 V) from a CPU thermistor 
> imput or at least a few different speeds.

The fan will get the voltage it needs to keep the temperature at 
reasonable levels. It usually kicks in at about 56 C (on the PowerBook) 
and is not loud at the lowest setting. The PowerBook actually is more 
quiet than the iBook.

It slowly (stepless) increases speed until it gets terribly loud. The 
PowerBook sounds like a small jetplane. The iBook sounds different. The 
iBook does not get as hot as the PowerBook. When the PB gets really 
hot, like when you are playing two movies on separate screens (with an 
external monitor connected) the GPU can reach 85+ C, and you can hurt 
yourself by touching the bottom of the PowerBook. (If I lived in the 
USA maybe I would have sued someone...)

It does not die however. My PowerBook has been in bed a lot (it's not 
as bad as it sounds) and it has got really, really hot sometimes.

When running dnetc on an iBook the fan rarely kicks in at all, unless 
it's sitting (or whatever an iBook does) on the bed. The PowerBook is 
unable to run dnetc, or anything using 100% CPU for a long time, 
without the need for some active cooling. The fan will usually run 
slowly, though.

>
>> There could also be things to lower your clock speed (I think the 
>> iBook does this when it goes into display sleep, because one morning 
>> the fan went on due to dnetc, which means it was running all night, 
>> without waking me up with the horribly loud fan).
>
> AFAIK the usual CPU energy saving technologies (Cool'n'Quiet, 
> PowerNow, SpeedStep, etc.) work by reducing the core 
> clock/multiplier/voltage when they detect low demand. They should not 
> touch the CPU if it's constantly at 100% utilization.

There are three settings on an iBook or PowerBook: "Automatic" 
(default), "Reduced" and "Highest". Automatic will clock the CPU down 
when it's not used very much (like now, when I am writing this mail) 
and run it at full speed when you are using it much. Setting it to 
"Reduced" means you are running at half the CPU speed all the time. 
"Highest" is... well, full speed all the time. If you monitor the 
temperature (with something like Hardware Monitor) you'll probably be 
disappointed though. You won't notice if the setting is "Highest" or 
"Reduced". The temperature is the same. So it obviously does something 
else to keep cool when not in use.

> In any case, my opinion about the thermal failure risk is that I'd 
> much rather have any machine, laptop or desktop, crash and burn when 
> it's just running Dnetc on its own than in the middle of me working on 
> something important with it. If it can't handle Dnetc, it needs to be 
> repaired/replaced anyhow.

I assume that the machine will simply turn itself off if it gets too 
hot. That's what the little white charger/net adapter does when it gets 
too hot: it will just go to sleep for a few minutes. Just put it under 
some blankets and you'll see. =)
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