It took Western Digital's HGST subsidiary more than a decade to develop a way to reliably seal helium gas inside of a hard drive. It was worth the wait. HGST Monday announced that it's now shipping a helium-filled, 3.5-inch hard disk drive with 50 percent more capacity than the current industry leading 4TB drives. The new drive uses 23 percent less power and is 38 percent lighter than the 4TB drives.