This is the number of days that you wish RMS to keep backup files. The default is 7 days. RMS will create one file per day. If you backup RMS more than once a day, the backup is overwritten. If you wish to have a more advanced backup plan, like multiple backups in one day or a transaction log, which would enable you to restore a database to the last activity before a crash, please refer to the Microsoft SQL Server documentation; you will need to perform these types of backups using the backup and restore capabilities available in Microsoft SQL Server.
NOTE: Microsoft SQL Server Express 2005 edition (available for no charge) does not have an agent that allows you to automate backups, you will need to purchase Microsoft SQL Server license for this.