How?
If two surfaces are flat enough and moving fast enough, the tiny amount of air (or helium these days) causes them to act hydrodynamically and float across each other which is great cause there's zero friction which means they never wear out.
The spindle in a hard drive is also an air bearing.
Re:Seagate Announces 16TB HDD
by captainperl on Wednesday December 05, 2018 @10:47PM
(#18615216)
Boundary-layer aerodynamics. The head is literally flying on a cushion of air.
Fun-fact: The "head fly height", i.e. the distance from the underside of the R/W head to the platter surface, is less than a handful nanometers in most hard drives; this makes the gap not just smaller than any production transistor, but also smaller than any production feature size.