As discussed in the section describing hard disk head
flying height, the old myth about hard disk heads and platters being "in a sealed
vacuum" or whatnot, is wrong in two ways: there's no vacuum in there, and the drive
itself isn't sealed, at least not in the way most people believe. In fact, air is
an essential component for proper drive operation. Regular hard disks aren't totally
sealed from the outside air, but they definitely are separated from it, in order to ensure
that the dirt and dust of the outside air is kept away from the delicate platters and
heads of the drive. If foreign matter were to get onto the platters--even something as
small as smoke particles--a head crash or other
problems could easily result.
Hard disks aren't sealed, because they have to be able to pass air between the inside
of the drive and the outside, in order to equalize any air pressure differential that may
exist between the two environments. This allows the disk to maintain proper equilibrium
when the weather changes, or the drive is moved to a different altitude; if pressure is
not balanced the drive might not perform properly and damage could even result. You can
actually see the small breather holes in the cases of many drives, placed there
for this purpose. Of course just putting a hole in the case would cause contamination of
the drive, so the holes are covered with a breather filter which lets air pass
through slowly but not dirt or dust. These filters are placed permanently and do not need
to be serviced or replaced.
|
Closeup shot of the breather holes in the top
of a hard disk case. Part of the breather
filter can be seen just under the holes. |
Hard disks also have an internal air flow within their sealed chambers (caused
by the rotation of the platters--there is no fan inside a hard disk). This air flow is
used to continuously filter the air within the disk assembly. Despite building the hard
disks in ultra-clean facilities and taking other precautions during manufacturing, a small
recirculating filter is built into the drive itself as an added security measure.
This filter is designed to work on the air that flows within the hard disk assembly,
catching any minute bits of debris that might somehow make it inside. This reduces the
chances that such dirt will end up on the disk platters. Like the breather filter, the
recirculating filter is not changeable, nor does it need to be.
|
A recirculating filter in the top cover of a
consumer-grade hard disk. |
Next: Orientation and Mounting
