 Teradata systems were the first to store and analyze 1 terabyte of data in 1992.Hard disk drives were 2.5 GB in 1991 so the definition of big data continuously evolves according to Kryder's Law.Teradata installed the first petabyte class RDBMS based system in 2007. , there are a few dozen petabyte class Teradata relational databases installed, the largest of which exceeds 50 PB.