DDC Fixed Head Disks
Billy.Pettit at wdc.com
Mon Jun 11 12:54:27 CDT 2007
dwight elvey wrote:
The only two things I can think of where mentioned by others. One
was thermal conductivity and the other was friction. Helium has almost
Still, the stuff leaks out of things so fast. Even solid surfaces.
I find it funny that it is cheaper than argon. There is a lot of
argon but I'd guess the extraction from natural gas, where it
is undesired for burning, makes helium cheaper than argon that has to
be intentionally removed from air. Two percent of air is argon
as I recall.
Helium was used in a lot of early fixed disk and drum systems. There were
several reasons for helium, but the main one is it gives good flying head
support. Less dense than air, it allowed the heads to fly closer. It also
offered less resistance than air, hence less power. And there was something
about it having less boundary layer pressure at high speed, a good thing
when you are trying to increase density.
It was a bitch to seal in, so most systems sealed the entire assembly with
only I/O cable connectors on the outside surface. I worked on a drum system
using helium in the late 1960s and we had to change the cylinder about once
a month. The cylinder was 20 cubic feet.
One other application I heard of was for high altitude airborne systems.
The air was too thin so a positive pressure system was used with helium.
Since the application was military, not much was written about it. This was
also the same application that used a micro drum (roughly 3 inches long, 1
inch in diameter.).
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