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The amount of collected data has grown tremendously. A first reason is because computers became ubiquitous around the $1980\text{'}$s and can easily record data. More recently, the world$-$wide web became ubiquitous in the early $2000\text{'}$s$,$ transforming how people do business, communicate, and recreate, in ways such that data is easily recorded and analyzed.

Smartphones and tablets of the $2010\text{'}$s provide nearly continuous computer$/$web access. Plus, numerous items like streets, cars, and buildings have recently been equipped with sensors and cameras and allowing for more data collection. Some estimates are that $90\%$ of all data ever collected was generated in just the past couple years.

The figure below shows the worldwide data collected per year, in zettabytes. A zettabyte is one sextillion or ${10}^{21}$ bytes. The table below lists common sources of data.