What? The first 4TB enterprise hard drive was just released. This is more or less where we should be at:
http://zedequalszee.files.wordpress.com/2009/06/hd-vs-year.jpgWe hit 1TB in 2009 and it looks like we'll be at 5+ TB by 2013... Sure looks like exponential growth to me.
From the wiki:
2007 First 1 terabyte hard drive[16] (Hitachi GST)
2008 First 1.5 terabyte hard drive[17] (Seagate)
2009 First 2.0 terabyte hard drive[18] (Western Digital)
2010 First 3.0 terabyte hard drive[19][20] (Seagate, Western Digital)
2010 First Hard Drive Manufactured by using the Advanced Format of 4 KiB a block instead of 512 bytes a block[21]
2011 First 4.0 terabyte hard drive[22] (Seagate)
Kinda looks like a doubling every two years-ish, no?