what is the name of the physical database file in which all directory data is stored?
Windows 2000 Active Directory data store, the actual database file, is %SystemRoot%\ntds\NTDS.DIT. The ntds.dit file is the heart of Active Directory including user accounts. Active Directory's database engine is the Extensible Storage Engine ( ESE ) which is based on the Jet database used by Exchange 5.5 and WINS. The ESE has the capability to grow to 16 terabytes which would be large enough for 10 million objects.