Every time I buy a new PC, either desktop or notebook, its hard disk capacity is larger than the previous one even though the total price of the PC is about equal. The same thing may apply for the other components of the PC like main memory capacity and CPU power, but hard disk capacity is something very different.

Matthew Komorowski has collected hard drive capacity/price data and created the graph below:

Source: http://www.mkomo.com/cost-per-gigabyte

Komorowski has also drawn a conclusion about the capacity/cost trend as:

Over the last 30 years, space per unit cost has doubled roughly every 14 months (increasing by an order of magnitude every 48 months)

Moreover, he has a formula for the cost as

*cost = 10*^{-0.2502(year-1980)+6.304}Below are two pictures from computer magazines of 80s. Incredible!