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“The most popular formulation is of the doubling of the number of transistors on integrated circuits (a rough measure of computer processing power) every 18 months. At the end of the 1970s, Moore’s Law became known as the limit for the number of transistors on the most complex chips. However, it is also common to cite Moore’s Law to refer to the rapidly continuing advance in computing power per unit cost.

A similar law has held for hard disk storage cost per unit of information. The rate of progression in disk storage over the past decades has actually sped up more than once, corresponding to the utilization of error correcting codes, the magnetoresistive effect and the giant magnetoresistive effect. The current rate of increase in hard drive capacity is roughly similar to the rate of increase in transistor count. However, recent trends show that this rate is dropping, and has not been met for the last three years. See Hard disk capacity.

Another version states that RAM storage capacity increases at the same rate as processing power.”[1]

[1] http://en.wikipedia.org/wiki/Moore%27s_law