Sign in with
Sign up | Sign in
Your question

Are hard drives hermetically sealed?

Last response: in Storage
Share
Anonymous
a b G Storage
April 26, 2004 1:17:04 PM

Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

Are hard drives hermetically sealed?

Reason I ask is I use an air purifier that puts out neg. ions and ozone. And
ozone will corrode computer parts, make them brittle. Especially a rubber
drive belt in a CD or DVD player. I think most components are impervious
enough and computer will be obsolete before the part fails.

But I wonder about hard drives. No one wants to have one fail. So I don't
want the ambient air entering the vitals of the hard drive.



Many thanks
Fens
Anonymous
a b G Storage
April 26, 2004 1:28:59 PM

Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

In article <Evednbf8RsIClhDdRVn-gg@comcast.com>,
fenceerx <spamonot@comcast.net> wrote:
>Are hard drives hermetically sealed?
>
>Reason I ask is I use an air purifier that puts out neg. ions and ozone. And
>ozone will corrode computer parts, make them brittle. Especially a rubber
>drive belt in a CD or DVD player. I think most components are impervious
>enough and computer will be obsolete before the part fails.
>
>But I wonder about hard drives. No one wants to have one fail. So I don't
>want the ambient air entering the vitals of the hard drive.
>
>
>
>Many thanks
>Fens
>
>


This was talked to death a couple of months ago in a usenet group,
either pc-hardware or storage related. Google will dig it all up.

The short answer is that disks have a single tiny hole with a
micron-level filter that serves to keep air pressure equilibrium
between the inside and the world. The net amount of air that gets thu
it is zero.

If the ozone level is high enough to rot rubber you're living
in a toxic zone;

" Ozone is highly injurious and lethal in experimental animals at
concentrations as low as a few parts per million (Stokinger
1957/Ex. 1-97) ........."

http://www.cdc.gov/niosh/pel88/10028-15.html


--
Al Dykes
-----------
adykes at p a n i x . c o m
Anonymous
a b G Storage
April 26, 2004 2:13:22 PM

Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

"fenceerx" wrote:
> Are hard drives hermetically sealed?


Maxtor's ATA hard drives are not hermetically sealed.
I called Maxtor, and I talked the technical support
supervisor into contacting their engineering staff at
headquarters. An hour later I got this answer by
telephone call-back:

Maxtor's drives are not hermetically sealed.
They have access to ambient air via a filter.
The altitude restriction is 10,000 feet.
The reason is for cooling.


*TimDaniels*
Related resources
Anonymous
a b G Storage
April 26, 2004 3:23:15 PM

Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

I shall check out the google archives. Many thanks. Ozone is a bit
different, killing the CD/DVD player drive belt over years of exposure and
maybe not at all.

Fens



"Al Dykes" <adykes@panix.com> wrote in message
news:c6j2qr$cuu$1@panix3.panix.com...
> This was talked to death a couple of months ago in a usenet group,
> either pc-hardware or storage related. Google will dig it all up.
>
> The short answer is that disks have a single tiny hole with a
> micron-level filter that serves to keep air pressure equilibrium
> between the inside and the world. The net amount of air that gets thu
> it is zero.
>
> If the ozone level is high enough to rot rubber you're living
> in a toxic zone;
>
> " Ozone is highly injurious and lethal in experimental animals at
> concentrations as low as a few parts per million (Stokinger
> 1957/Ex. 1-97) ........."
>
> http://www.cdc.gov/niosh/pel88/10028-15.html
>
>
> --
> Al Dykes
> -----------
> adykes at p a n i x . c o m
Anonymous
a b G Storage
April 26, 2004 3:57:49 PM

Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

In article <QLudnVA79_KPtBDd4p2dnA@comcast.com>,
fenceerx <spamonot@comcast.net> wrote:
>
>I shall check out the google archives. Many thanks. Ozone is a bit
>different, killing the CD/DVD player drive belt over years of exposure and
>maybe not at all.
>
>Fens


What's Different ? Here's another health and saftey
datasheet. If your generator is exceeding 0.1ppm ozone
you can sue yourself.

http://www.state.nj.us/health/eoh/rtkweb/1451.pdf

>
>
>
>"Al Dykes" <adykes@panix.com> wrote in message
>news:c6j2qr$cuu$1@panix3.panix.com...
>> This was talked to death a couple of months ago in a usenet group,
>> either pc-hardware or storage related. Google will dig it all up.
>>
>> The short answer is that disks have a single tiny hole with a
>> micron-level filter that serves to keep air pressure equilibrium
>> between the inside and the world. The net amount of air that gets thu
>> it is zero.
>>
>> If the ozone level is high enough to rot rubber you're living
>> in a toxic zone;
>>
>> " Ozone is highly injurious and lethal in experimental animals at
>> concentrations as low as a few parts per million (Stokinger
>> 1957/Ex. 1-97) ........."
>>
>> http://www.cdc.gov/niosh/pel88/10028-15.html
>>
>>
>> --
>> Al Dykes
>> -----------
>> adykes at p a n i x . c o m
>
>


--
Al Dykes
-----------
adykes at p a n i x . c o m
Anonymous
a b G Storage
April 26, 2004 9:22:26 PM

Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

I wonder why they said it is for cooling? Not much, if any, air moves
through this filter.

--Dan

"Timothy Daniels" <TDaniels@NoSpamDot.com> wrote in message
news:fLCdner4u6at3hDdRVn-tA@comcast.com...
>
> "fenceerx" wrote:
> > Are hard drives hermetically sealed?
>
>
> Maxtor's ATA hard drives are not hermetically sealed.
> I called Maxtor, and I talked the technical support
> supervisor into contacting their engineering staff at
> headquarters. An hour later I got this answer by
> telephone call-back:
>
> Maxtor's drives are not hermetically sealed.
> They have access to ambient air via a filter.
> The altitude restriction is 10,000 feet.
> The reason is for cooling.
>
>
> *TimDaniels*
Anonymous
a b G Storage
April 26, 2004 9:22:27 PM

Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

In article <mzbjc.41313$ga4.19767@newssvr29.news.prodigy.com>,
dg <dan_gus@hotmail.com> wrote:
>I wonder why they said it is for cooling? Not much, if any, air moves
>through this filter.
>

The altitude limit is common for lots of sophisticated electronic
equipment. Circulating air's ability to remove heat is a function of
density (ie altitude.)

Heat has to be disapated from the spinning disk. ISTR that at 10K rpm,
for instance, essentially all the wattage that goes into the motor
gets turned into heat via aerodynamic drag on the surface of the disk.
I've also heard that, for some disks, a certain amount of air density
is necessary to float the flying heads.

There is essentially zero airflow thru the filter. It just keeps the
pressure equal to the ambient.


>--Dan
>
>"Timothy Daniels" <TDaniels@NoSpamDot.com> wrote in message
>news:fLCdner4u6at3hDdRVn-tA@comcast.com...
>>
>> "fenceerx" wrote:
>> > Are hard drives hermetically sealed?
>>
>>
>> Maxtor's ATA hard drives are not hermetically sealed.
>> I called Maxtor, and I talked the technical support
>> supervisor into contacting their engineering staff at
>> headquarters. An hour later I got this answer by
>> telephone call-back:
>>
>> Maxtor's drives are not hermetically sealed.
>> They have access to ambient air via a filter.
>> The altitude restriction is 10,000 feet.
>> The reason is for cooling.
>>
>>
>> *TimDaniels*
>
>


--
Al Dykes
-----------
adykes at p a n i x . c o m
Anonymous
a b G Storage
April 26, 2004 9:22:28 PM

Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

"Al Dykes" wrote:
>
> The altitude limit is common for lots of sophisticated electronic
> equipment. Circulating air's ability to remove heat is a function of
> density (ie altitude.)
>
> Heat has to be disapated from the spinning disk. ISTR that at 10K rpm,
> for instance, essentially all the wattage that goes into the motor
> gets turned into heat via aerodynamic drag on the surface of the disk.
> I've also heard that, for some disks, a certain amount of air density
> is necessary to float the flying heads.
>
> There is essentially zero airflow thru the filter. It just keeps the
> pressure equal to the ambient.


There is another reason for altitude restrictions, but they apply
for higher voltages such as those found in a switching power supply.
This has to do with arcing. When the air separating two electrical
potentials is dense, any ionization caused by cosmic rays will
quickly be quenched before the ionized gas particles can accelerate
to a speed (i.e. before they can attain a kinetic energy high enough)
to cause more ionization in an effect known as "avalanche discharge".
When the air gets rarified, though, this quenching effect diminishes,
and at some point of rarification, it is not enough to prevent
avalanching, and the electrical circuitry is effectively short-circuited.
This avalanching and hermetic seals to prevent it (along with cooling
requirements) are important engineering problems for designers of
electronic gear used in high-altitude airplanes and spacecraft. In the
case of a hard disk drive, there is the added requirement of air density
high enough to sustain separation of the flying read/write head above
the surface of the spinning platter. Which requirement - cooling or
head levitation - is really responsible for the 10,000 ft. requirement
may have been lost in the translation between Maxtor's engineering
staff and its technical support supervisor. The website for the
Keck observatory on Hawaii's 13,800 ft. high Mauna Kea does
mention that air pressure there is only 60% of that at sea level. An
interesting statement is this:

"A four-wheel-drive vehicle is required beyond the 9,200 foot
level as the air is too thin to adequately cool a vehicle's brakes
upon descent."

*TimDaniels*
April 26, 2004 11:20:55 PM

Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

I was looking into a project some time ago in which a hard drive was
required to operate at high atmospheric pressure and I was concerned
about how the aerodynamic design of the platter/head would be
affected. Low pressure at 10,000 feet would similarly upset the drive
if my concern was with any merit.

Does anyone have any knowledge in this issue?
Anonymous
a b G Storage
April 26, 2004 11:20:56 PM

Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

"Peter" wrote:
> I was looking into a project some time ago in which a hard drive was
> required to operate at high atmospheric pressure and I was concerned
> about how the aerodynamic design of the platter/head would be
> affected. Low pressure at 10,000 feet would similarly upset the drive
> if my concern was with any merit.
>
> Does anyone have any knowledge in this issue?

I just called the assistant administrator at the Keck Observatory
in Waimea, Hawaii. He says that they haven't had any problems
with PCs operating at the observatory at the summit (almost 14,000 ft).
On the other hand, the temperature at the observatory is considerably
lower than at sea level, and cooling problems may be compensated by
the effects of the lower temperatures. The administrator said that he
knew of no head crashes due to altitude in their PC hard drives.

*TimDaniels*
Anonymous
a b G Storage
April 27, 2004 2:35:55 AM

Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

On Mon, 26 Apr 2004 11:23:15 -0400, "fenceerx" <spamonot@comcast.net>
wrote:

>
>I shall check out the google archives. Many thanks. Ozone is a bit
>different, killing the CD/DVD player drive belt over years of exposure and
>maybe not at all.

DVD and CD players don't have anything as sloppy as rubber drive belts, do
they? I don't remember any on the ones I've taken apart.

--
Michael Cecil
http://home.comcast.net/~macecil/
Anonymous
a b G Storage
April 27, 2004 3:05:57 AM

Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

Peter wrote:

> I was looking into a project some time ago in which a hard drive was
> required to operate at high atmospheric pressure and I was concerned
> about how the aerodynamic design of the platter/head would be
> affected. Low pressure at 10,000 feet would similarly upset the drive
> if my concern was with any merit.
>
> Does anyone have any knowledge in this issue?

I don't have any specific information about the aerodynamic issue however
there are hermetically sealed drives available that are primarily used for
military applications. One of those may suit your purpose better than one
of the mass-market drives. Contact the manufacturers.

--
--John
Reply to jclarke at ae tee tee global dot net
(was jclarke at eye bee em dot net)
Anonymous
a b G Storage
April 27, 2004 4:53:47 AM

Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

In article <1ikq80da951n3e7quogsil6i8dedm6di5q@4ax.com>,
Peter <usenet_AT_tecno.demon.co.uk@JUNKBLOCK.COM> wrote:
>I was looking into a project some time ago in which a hard drive was
>required to operate at high atmospheric pressure and I was concerned
>about how the aerodynamic design of the platter/head would be
>affected. Low pressure at 10,000 feet would similarly upset the drive
>if my concern was with any merit.
>
>Does anyone have any knowledge in this issue?

You might find that different models have different
max altitude specs. It's on the manufacturer's web site.

I'm guessing that 2.5 inch disks may have wider operating
regions since most of them go into portable consumer equipment.


--
Al Dykes
-----------
adykes at p a n i x . c o m
Anonymous
a b G Storage
April 27, 2004 4:56:43 AM

Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

In article <mzbjc.41313$ga4.19767@newssvr29.news.prodigy.com>,
dg <dan_gus@hotmail.com> wrote:
>I wonder why they said it is for cooling? Not much, if any, air moves
>through this filter.
>

Heat transfer by conduction, not air exchange.

--
Al Dykes
-----------
adykes at p a n i x . c o m
Anonymous
a b G Storage
April 27, 2004 12:34:26 PM

Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

Many thanks for your answer and the others who posted advice and answers.

Fens


"Timothy Daniels" <TDaniels@NoSpamDot.com> wrote in message
news:fLCdner4u6at3hDdRVn-tA@comcast.com...
>
> "fenceerx" wrote:
> > Are hard drives hermetically sealed?
>
>
> Maxtor's ATA hard drives are not hermetically sealed.
> I called Maxtor, and I talked the technical support
> supervisor into contacting their engineering staff at
> headquarters. An hour later I got this answer by
> telephone call-back:
>
> Maxtor's drives are not hermetically sealed.
> They have access to ambient air via a filter.
> The altitude restriction is 10,000 feet.
> The reason is for cooling.
>
>
> *TimDaniels*
Anonymous
a b G Storage
April 27, 2004 12:42:05 PM

Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

"Michael Cecil" <macecil@comcast.net> wrote in message
news:2l3r80dcks9d5m4np6irbd5umbo6l2fccs@4ax.com...
> On Mon, 26 Apr 2004 11:23:15 -0400, "fenceerx" <spamonot@comcast.net>
> wrote:
>
> >
> >I shall check out the google archives. Many thanks. Ozone is a bit
> >different, killing the CD/DVD player drive belt over years of exposure
and
> >maybe not at all.
>
> DVD and CD players don't have anything as sloppy as rubber drive belts, do
> they? I don't remember any on the ones I've taken apart.
>
> --
> Michael Cecil
> http://home.comcast.net/~macecil/



My fault for not being accurate. I had a DVD player that failed 3 years ago.
Took it apart and there was a drive belt for the eject mechanism.

Not a belt for driving the CD or DVD, making it spin.

Fens
April 27, 2004 10:02:07 PM

Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

<< Not a belt for driving the CD or DVD, making it spin.

Fens >>




Some do, believe it or not.

Surprisingly, belt drives are not bad or sloppy for this job.


--
Dr. Nuketopia
Sorry, no e-Mail.
Spam forgeries have resulted in thousands of faked bounces to my address.
Anonymous
a b G Storage
April 28, 2004 1:50:11 AM

Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

"Al Dykes" <adykes@panix.com> wrote in message news:c6kp6b$ad0$1@panix3.panix.com
> In article <mzbjc.41313$ga4.19767@newssvr29.news.prodigy.com>,
> dg <dan_gus@hotmail.com> wrote:
>> I wonder why they said it is for cooling? Not much, if any, air moves
>> through this filter.
>>
>
> Heat transfer by conduction, not air exchange.

ROTFLOL!

>
> --
> Al Dykes
> -----------
> adykes at p a n i x . c o m
Anonymous
a b G Storage
April 28, 2004 5:32:16 AM

Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

In article <c6memr$dgqlu$1@ID-79662.news.uni-berlin.de>,
Folkert Rienstra <folkertdotrienstra@freeler.nl> wrote:
>"Al Dykes" <adykes@panix.com> wrote in message
news:c6kp6b$ad0$1@panix3.panix.com
>> In article <mzbjc.41313$ga4.19767@newssvr29.news.prodigy.com>,
>> dg <dan_gus@hotmail.com> wrote:
>>> I wonder why they said it is for cooling? Not much, if any, air moves
>>> through this filter.
>>>
>>
>> Heat transfer by conduction, not air exchange.
>
>ROTFLOL!
>


Huh ????


--
Al Dykes
-----------
adykes at p a n i x . c o m
Anonymous
a b G Storage
April 28, 2004 4:17:56 PM

Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

Al Dykes wrote:
> In article <c6memr$dgqlu$1@ID-79662.news.uni-berlin.de>,
> Folkert Rienstra <folkertdotrienstra@freeler.nl> wrote:
>
>
>>ROTFLOL!
>>
>
> Huh ????

Rolling On The Floor Laughing Out Loud
April 28, 2004 8:36:55 PM

Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

Seymour Dupa wrote:
>
>
> Al Dykes wrote:
>
>> In article <c6memr$dgqlu$1@ID-79662.news.uni-berlin.de>,
>> Folkert Rienstra <folkertdotrienstra@freeler.nl> wrote:
>>
>>
>>> ROTFLOL!
>>>
>>
>> Huh ????
>
>
> Rolling On The Floor Laughing Out Loud
>
I think he knows what it means. But it didn't fit the context.


--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form che...@prodigy.net.
Anonymous
a b G Storage
April 29, 2004 4:02:20 AM

Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

"Al Dykes" <adykes@panix.com> wrote in message news:c6nfl0$prt$1@panix3.panix.com...
> In article <c6memr$dgqlu$1@ID-79662.news.uni-berlin.de>, Folkert Rienstra <> wrote:
> >"Al Dykes" <adykes@panix.com> wrote in message news:c6kp6b$ad0$1@panix3.panix.com
> > > In article <mzbjc.41313$ga4.19767@newssvr29.news.prodigy.com>, dg <dan_gus@hotmail.com> wrote:
> > >
> > > > I wonder why they said it is for cooling? Not much, if any, air moves
> > > > through this filter.
> > > >
> > >
> > > Heat transfer by conduction, not air exchange.
> >
> > ROTFLOL!
> >
>
>
> Huh ????

Yeah, Huh!

And fix your newsclient, you are spreading reply addresses
all around the internet for any virus and spam spreaders to see.

>
>
> --
> Al Dykes
> -----------
> adykes at p a n i x . c o m
Anonymous
a b G Storage
April 29, 2004 5:14:47 AM

Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

I think the 10,000ft altitude is for reasons of air density:
o At altitude you will move the same cfm of air
o However due to lower density the mass of air moved is less

For 10,000ft that reduction in actual mass of air is large.

Whilst the drive has a max temp of say 52 or 55oC, some
components on the PCB have a higher temperature - such as
motor drive ic's. So whilst the drive may be in spec, you can
have components out of spec. A drive tends to have a spec
airflow in m/sec over its surface - which is your m^3 through
a particularly cross-sectional area. You would have to adapt
the m/sec airflow for that at your an altitude, eg, 10,000-ft.

I think there may be something in the head flying over the disc,
but you'd have to perhaps dig someone out of IBM Almaden.

At really high altitude, you're talking about aviation integration,
and that brings into play other design factors - re ruggedness,
sealed NEMA enclosures, ability to withstand fogging, things
like condensation, shock, vibration, and lots of other nasties.

Could also be a more practical reason for a 10,000ft limit:
o Argument may be head-flying or cooling re air mass/density
o Argument could equally be one of not testing to say 75,000ft :-)

Exactly how many users are going to be operating a hard drive in
an unpressurised aircraft at altitudes above 10,000ft? Sit on top
of a U2 operating your laptop with the wind in your hair? :-)

That could be a real bad hair day.

Still, it would be interesting to know what the spec is for a laptop
disk - you could want to email someone from the top of Everest.
"Honey, I think I left the gas on - could you just pop home & check?".
In that instance I'm sure an explorer reported that HD didn't work.

Either that or he'd forgotten to charge the battery... ...
--
Dorothy Bradbury
April 29, 2004 4:48:04 PM

Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

My application was a deep sub-sea project at very high pressures. I
can guess that at high pressure the air will turn to liquid and that
will certainly stop the drive working. And in a vacuum the head will
simply scrape over the surface of the disc as there will be no
aerodynamic behavior at all. Somewhere in the middle a disc drive
operates within spec.
April 30, 2004 3:54:34 AM

Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

Actually 10,000 ft is not extreme altitude. Quite a few people
live at that level.

When trekking in Nepal I have done emails in Internet cafés
(satellite), at Namche Bazaar, which is at some 12,000 ft. They
had some fairly new desktops and at least one well used
Thinkpad. I am sure the HD´s were just plain ordinary.

I also know that at Everest Base Camp, abt 18,000 ft, the
expedition base camp crews send out emails daily.
If I remember correctly it is mentioned in the book "Into Thin
Air" (great book!), that a jet set American female climber had
porters lug her Thinkpads, and quite a supply of batteries,
almost all the way to the top of Everest. At least to camp 7,
at some 25,000 ft, so that she could write her diary in style.

I believe that at 18,000 ft the air is about half as dense as
at sea level. It seems to be enough for a lap top.


On Thu, 29 Apr 2004 01:14:47 +0100, Dorothy Bradbury wrote:

>Exactly how many users are going to be operating a hard drive in
>an unpressurised aircraft at altitudes above 10,000ft? Sit on top
>of a U2 operating your laptop with the wind in your hair? :-)
>
>That could be a real bad hair day.
>
>Still, it would be interesting to know what the spec is for a laptop
>disk - you could want to email someone from the top of Everest.
>"Honey, I think I left the gas on - could you just pop home & check?".
>In that instance I'm sure an explorer reported that HD didn't work.
>
>Either that or he'd forgotten to charge the battery... ...


Lars
Stockholm
Anonymous
a b G Storage
April 30, 2004 6:07:08 AM

Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

Peter wrote:

> My application was a deep sub-sea project at very high pressures. I
> can guess that at high pressure the air will turn to liquid and that
> will certainly stop the drive working. And in a vacuum the head will
> simply scrape over the surface of the disc as there will be no
> aerodynamic behavior at all. Somewhere in the middle a disc drive
> operates within spec.

If you're going to be designing systems to work at high pressure, you need
to familiarize yourself with the physics of the situation before you do
anything.

Air will not liquefy at _any_ pressure until the temperature gets below the
critical temperature of one of its components, and the critical
temperatures for all the major components of air are more than 100C below
the freezing point of sea water.

When you are doing engineering, do not _guess_.

At that kind of pressure I doubt that the sealed mil-spec drives would hold
up--while they'll take some pressure they aren't designed for those levels.
You need to either make a pressure vessel to hold the drives or you need to
go to an alternative technology that is not dependent on a specific range
of air pressures.

--
--John
Reply to jclarke at ae tee tee global dot net
(was jclarke at eye bee em dot net)
Anonymous
a b G Storage
April 30, 2004 8:09:55 AM

Archived from groups: comp.sys.ibm.pc.hardware.storage (More info?)

You may be able to use a flash memory drive of some kind. I don't know the
operating specs of them but I would guess that they may be more tolerant to
more extreme pressure levels. While they won't have issues with
aerodynamics of a head passing over a platter, they might have some other
limitation.

--Dan

"Peter" <usenet_AT_tecno.demon.co.uk@JUNKBLOCK.COM> wrote in message
news:gkq1909jnqtuthppmlprr13v8bno4og4uo@4ax.com...
> My application was a deep sub-sea project at very high pressures. I
> can guess that at high pressure the air will turn to liquid and that
> will certainly stop the drive working. And in a vacuum the head will
> simply scrape over the surface of the disc as there will be no
> aerodynamic behavior at all. Somewhere in the middle a disc drive
> operates within spec.
!