Why helium?
Well, helium being a very light gas (only hydrogen is less dense), is obviously dust and moisture free and is also chemically inert. As a result the lifetime of the drive should be a lot longer and also friction within the bearings is lower so self heating is less of an issue.
I've also read somewhere that if hydrogen were used there would be deleterious effects on the data layers as H2 can induce cracking in some alloys.
Incidentally helium is also apparently used in Philips LED light bulbs to conduct heat from the "filament" to the outside air more efficiently.
Biting the hand that feeds IT
