Extensible Storage Engine
Active Directory is implemented on top of an Indexed Sequential Access Method (ISAM) table manager, historically called "Jet." This same table manager is used by Exchange, File Replication service (FRS) the security configuration editor, Certificate Services, Windows Internet Name Service (WINS), and various other Windows components. In Windows 2000, this table manager is referred to as the Extensible Storage Engine (ESE).
The ESE (Esent.dll) database uses a concept of discrete transactions and log files to ensure the integrity of Active Directory. Each request to the DSA to add, modify, or delete an object or attribute is treated as an individual transaction. As these transactions occur on each domain controller, they are recorded in a series of log files that are associated with each Ntds.dit file. By default, the Active Directory database file is stored on < drive >\winnt\NTDS\Ntds.dit. Likewise by default, the log files are stored in the same directory.