About SQL Server database backups

The following types of backup operations can be performed on databases:

Full	The database, including all of its component files are backed up as a single image. The log file is included in a full database backup. Note: The transaction log is not automatically truncated following a full backup. Thus a common practice to preserve disk space is to manually truncate the transaction log following a successful full backup.
Differential	All of the changes since the last full are backed up to a single image.
Transaction log	Transaction log backups are only available for the full and bulk-load recovery options. In this operation, the inactive portion of the transaction log is backed up. The following options are available when you select transaction log backup: Back up and truncate transaction log Back up transaction log, but do not truncate it Back up and restore tail log (legacy SQL Server backup policies) The last option is a backup but it does not create a permanent backup image. A typical use of this type of transaction log backup is: after a page-level restore when the database is recovered, but all of the filegroups have not been brought back on line. By backing up and recovering the tail end of the log, SQL Server is able to bring the database back to a usable state.