Vacuum = requires special lubricants or no lubricants at all, since they would dissipate due to the lowered vapour pressure. Lubricant everywhere would likely b

Vacuum = requires special lubricants or no lubricants at all, since they would dissipate due to the lowered vapour pressure. Lubricant everywhere would likely be problematic. It's also harder to seal in, and would likely require a much more rigid construction to avoid warping of the drive (these are precision devices after all). Lastly, the hovering of the R/W heads over the platters requires an atmosphere - they are lifted by the air/gas accelerated by the platters (this is a well defined lift force and self-regulates the head height relative to the platter).