SQL Server 2000 allows three types of database files

Primary data files: Every database has one primary data file. This file contains the startup information for the database and is used to store data. The name of primary database file has the extension MDF.

Secondary data files: These files hold all of the data that does not fit into the primary data file. A database can have Zero or more Secondary data files. The name of scondary database file has the extension NDF.

Transaction Log files: These files hold the log information used to recover the database. There must be at least one log file for each database. The name of a Log file has the extension LDF.

SQL Server 2000 allows three types of database files