The massive density was demoed by Segate at the IDEMA DISKCON show this week. While 421Gbpsi may sound like ans abstract number, let me put it into a little more perspective for you. It means 40GB 1 inch drives, 275GB 1.8", 500GB laptop 2.5" and 2.5TB 3.5" desktop parts are possible.
Seagate thinks they will have them ready by 2009. µ