I periodically check on the retail price of storage. The one terabyte (one trillion bytes) drive is a good indicator.

The last column of my updated "Terabyte Update" table shows how much more a single TB drive costs than two 500GB drives on a per/GB basis. In the last year, the 1TB drive crossed over and became more economical than dual 500s.

Hard disk drives continue to batter Moore's law, which predicts that the 1TB drive would cost $113 in May, 2010.

For comparison, here is the approximate cost per gigabyte of a other storage types: 250GB solid state memory drive, $2.76; flash memory such as that used for cameras, $9; and contemporary DDR3 RAM, $25.