The price of memory.
In the 1980s a 4MB memory upgrade for a Sun Workstation cost $1,000.
This 2 MB RAM memory upgrade kit sold for $100, or $50/MB in 1997. Accouning for inflation this RAM would now cost $69.21/MB in 2011.
A 4GB memory upgrade can be purchased now (2011) for about $44, or $0.011/MB or .0001% of the cost in 1997.