>> seminars, however, I have run various hard disks for days with
>> the lids off, and have even removed and installed the covers
>> while the drives were operating. Those drives continue to store
>> data perfectly to this day with the lids either on or off. Of course
>> I do not recommend that you try this with your own drives ; neither
>> would I use it on my larger, more expensive, drives"

>I have done this.  I took an old 20Mb drive and removed the cover.  I had
it
>sitting in my office running continuous chkdsk's (dos, remember?)  It ran
>for weeks with no dust protection.  I even blew cigarette smoke at it, and
>that never phased it a bit.  Finally, after several weeks, it started to

The reason you can do this with minimal problems is the airflow within the
drive. The air is drawn through a particle filter then up the spindle and
out across the platters. This, along with the centrifugal action of the
spinning platters will keep most particles away from where they can do
damage, unless the heads are at the outer limits and you manage to blow hard
enough to get particles onto the inner area of the platter where they will
then proceed outwards towards the heads.
The air is recirculated inside the sealed area with a pressure relief valve
to allow pressure equalisation with the outside air.

This system is also used on all hard disk drives that operate in free air,
but because of the possibility of having dirt particles on the disk surface
after the drive has been stopped for a while, there is always a purge period
where the drive is spinning before the heads are loaded. This period will
depend on the drive. I remember a 300MB exchangeable pack drive which would
be online in about 15 - 20 secs from a standing start, and everytime the
head stack did a seek over an appreciable number of tracks the floor would
shake.

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