Cost of Storage 

I added a new section on Cost of storage.  I hesitated to do this without discussing it first, however I have often seen statements of encouragement for people to be somewhat fearless in making contributions.  I feel that a section on cost is another way to add context to the understanding of the size of a terabyte.  Since this measurement (terabytes) is most commonly used with reference to disk drives and since there is already a section on disk drive capacity, it seemed reasonable that there should also be a context to show how the cost of that capacity has changed over time.  Does that make sense?  Now, if I could just remember how much I used to pay for a box of punched cards... ;-)