Extensible Storage Engine
Extensible Storage Engine (ESE), formerly known as JET, is a multi-user database that supports full Data Manipulation Language (DML) and Data Definition Language(DDL). ESE is optimized for fast retrieval of data since this is the main function that the database performs.
The underlying ESE database is stored in two files, one with extension .edb and the other with extension .stm . The data is these files is stored in the ESE file format. ESE also defines a low level API to the underlying database structures. The ESE API is used by Microsoft Exchange Server and other database such as Active Directory (Ntds.dit). Exchange 2000/2003 uses a version of ESE called ESE98, while Exchange 5.5 and Active Directory uses an older version called ESE97.