Laptop outside -> may cause condensation on hdd when going inside ?

[Peter]

Tyler Aviss <tjaviss at ...> writes:
...

thanks for sharing that.

I do have problems and I know they are bad (I am supposed to be wearing glasses
but I don't wear them in winter because I would spend six months wiping
condensation off of them every time I go inside).

Dew point is the temperature of an object at which water from the atmosphere
condenses on it. It forms a fogging layer on a lens and a deadly layer on a hard
drive when the heads which are supposed to be flying a few microns above the
platters plough into the water droplets condensed on it, creating furrows where
your data will have been. When an aircraft is colder then the dew point and it
flies through cloud it builds up so much ice that it falls down and kills a lot
of people. For this reason aviation weather pays extremely much attention to the
dew point, and 'icing conditions' (normally always when clear cold air leads to
warm moist air in the flight path). Similar problems apply to power lines (see
under 'freezing rain blackout' for details and recent examples).

Military and scientific equipment that is meant to withstand this is canned in
hermetic cans which are then blown with dry nitrogen or SF6 and also contain
desiccants. The result is extremely dry air or inert gas which will not yield
any dew inside no matter what is done to the box temperature-wise.

In their immense wisdom (and penny scrounging) hdd makers have opted for
non-hermetic cases (the little hole that says 'do not obstruct' is the
connection to ambient air on most hard disks). This makes the cases cheaper (it
will not try to blow up when you go up in an airplane and will not crumple or
implode if you visit a deep mine or the dead sea).

The short version: non-hermetic hdd's MUST be kept above the dew point at all
times, the dew point being their death point. Conventional wisdom requires
equipment that was exposed to cold to be allowed to adapt to the ambient
temperature before turning it on, unless it is protected against dew. That is
not an option when one walks outside with a laptop in a bag and then goes inside
and expects to use it asap.

The question was, how is this done by native canucks. I got some witty responses
on IRC #electronics etc. One of them involved putting the laptop close to one's
hairy body for warmth and pretending to have a *flat* rabbit in the pocket (one
run down by a truck?) in case someone asks.

Peter


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