Guys... You know that there's more than 1sq/in on a drive. You know that the stated (new density) is 1TB/sqin. So don't tell me that the capacity will be 16GB.
Also. Brett. Mate. I think you just multiplied the current density, by the area, to get current capacity. I like your thinking though. So lets try again
density * area = capacity
1 (TB per sq in) * 3.8 (sq in) = 3.8 TB. Better I think.
Now - for a multi-platter, multi side arrangement, we might expect four times that.