Pismo status

[Worth]

On Fri, 19 May 2000, Sergio Brandano wrote:

>
> >>  Sorry, I do not see your point.
> >>
> >>  My point is that if the CPU is piping hot, and you shutdown the
> >>  computer, no cooling is provided. This is wrong, as the fan has
> >>  nothing to do with the OS and it *must* spin until the temperature
> >>  reaches a safe level.
>
> >Well, the fan is there to remove the exess heat generated by a running CPU, if
> >you shut off the CPU, there will be no more exess heat generated, and the
> >existing heat will most assuredly be dissipated to less active cooling
> >mechanism. Since you cannot damage the CPU, or other pieces of the hardware,
> >this should cause no problem. And i think the G3 processor is not so hot
> >running, that it will be so much above the safe temperature state.
>
>  Ok Sven. You are convinced about your idea, but I am still skeptical.
>  In order to persuade me, I need a proof. Please perform this simple
>  experiment, then report the result. The experiment is as follows.
>  Have a nice and long trip with your car, then come back home, and
>  switch the engine off ensuring that the cooling fan is not spinning.
>  Let us know if your car starts again the next day.

Bad analogy, many cars have fans that don't run after shutdown and
they run fine every day (I've never owned own that was any other
way). The ones that run electric fans after shutdown tend to be highly
stressed small engines with thin-wall blocks in cramped engine
compartments with poor air flow and small capacity high-pressure cooling
systems. In such situations there is a potential for localized boiling of
stagnant coolant around hot spots in the block. This can result in
problems like accelerated corrosion, coolant overflow, and coolant vapor
lock. Running the fans helps to maintain some coolant movement by
convection and to also cool the enginecompartment to avoid fuel-line
vapor lock.

Notebooks, are a very different case, none are liquid cooled and
the temperature levels and differences between coolant and
components are not so extreme. Nor are you constrained by the
boiling point of the coolant and the batteries are not going
to vapor lock.

If you are worried about your Pismo:

1) Leave your screen up for a few minutes after shutdown if it seems
   unusually hot (frankly mine has never been anywhere near as hot as
   it gets just idling in MacOS -- fire up a DVD and you could roast
   marshmellows). Convection through the keyboard is the primary cooling
   mechanism, the fan isn't even secondary (and if it did run after
   shutdown, it would have very limited effectiveness with the screen
   down).

OR:

2) You are free to not run Linux, but you better not run Darwin either.
   Darwin also doesn't have any thermal management for any of the
   PowerBooks. The high-level abstract classes for thermal management,
   including fan speed control, are in the new Darwin IOKit, but no
   machine specific implementations -- yet. Even with the thermal
   management of the fan speed, all you gain is a bit of noise and perhaps
   power reduction for transient thermal increases. If the increased
   thermal load is sustained, the fan will eventually have to run full
   speed, which is what the PMU appearently does anyway as a fail-safe.


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