In a recent IHS analysis, WD's subsidiary development arm, Hitachi GST, have said that development of their 5.6TB helium based disk drives is well underway.
Helium, which is far lighter than air and the universes second most lightest element (we know of) is used inside the drive and produces less drag over the surface of the disks by the arm and can consume less power by up to 23%. The gas also conducts heat better which will improve the life span of the drive considerably. The technology could see WD putting in seven platters instead of five which means a 4TB five platter drive we have so far, could realise a 5.6TB capacity by using 800Gb per platter over seven platters. These combined elements of capacity, low power and long life span could result in a right kick in the teeth for Seagate.
The analysts also believe that the helium drive sales will go from zero to 100 million units in three years if the cost is right. This all assumes the form factor is still 3.5" and the availability of the inert gas.
And of course, this is all before the next generation of heat assisted magnetic recording is released.