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.
