What are the types of files used by SQL server databases ?

SQL Server databases use the following types of files: Primary Data File (.mdf): The primary data file contains the startup information for the database and points to other files in the database. User data and objects can be stored in this file or in secondary data files. Every database has one primary data file. The file extension used is '.mdf', an acronym for Main Data File. Secondary Data Files (.ndf): Secondary data files are optional, user-defined, and store user data. Secondary files can be used to spread data across multiple disks by putting each file on a different disk drive. Additionally, if a database exceeds the maximum size for a single Windows file, secondary data files can be used so that the database can continue to grow. The file extension used is '.ndf'. Transaction Log Files (.ldf): The transaction log files hold the log information that is used to recover the database. There must be at least one log file for each database. The file extension used is '.ldf'.