Helium drive
A hard drive hermetically sealed and filled with helium instead of air, to squeeze in more and thinner platters.
Helium has roughly one-seventh the density of air. That means the spinning platter stack meets less turbulence and drag, which in turn lets the maker stack more and thinner platters — seven in a 3.5-inch drive versus five in an air-filled one — and hold the heads steadier over the track. The bonus is lower power, cooler running and quieter operation.
HGST (then part of Western Digital) sold the first commercial helium drive in 2013: a 6 TB Ultrastar He6 under the HelioSeal brand. The seal is the hard part — helium is a small atom that loves to leak out, so the enclosure must be laser-welded tight for the drive's whole life. Today essentially every high-capacity drive is helium-filled, and the technology is a prerequisite for both SMR and dual actuators.