Relational Database Management Systems - RDBMS
Although most businesses manage their corporate data in relational database management systems (RDBMS), many businesses still operate application systems that use flat files for data storage. Many of these systems are legacy "batch" systems that can't support online data transactions. A flat file can be stored on computer tape or on a hard drive of some sort.
Network databases such as IDMS became popular in the 1980s, when computers were much less powerful than the ones that exist today. Although network databases supported online transactions, the databases were relatively inflexible. Once a database was designed, it was often costly to implement changes.
Hierarchical databases were also popular in the 1970s and 1980s.