When you install SQL Server several databases are created automatically. Two of the databases (Northwind and pubs) are sample user databases and can be used as examples or you can delete them safely (but they don’t take up a lot of hard disk space). The other four special system databases (master, model, msdb, and tempdb) are used by the system and should not be removed. To view the databases that are on your SQL Server, in Enterprise Manager expand the group your server is located in, then expand the server, and last expand the Databases folder. Remember, if you have the “Show system databases and system objects” checkbox unchecked in the SQL Server’s registration properties, you will be unable to see the system databases in Enterprise Manager.
master Database – Contains information about the server overall and all databases created. The information in this database includes: file allocations, disk space usage, system-wide settings, user accounts, and the existence of other databases and other SQL Servers.
model Database – This database provides a template for all newly created databases. If you ever need to add a table or stored procedures to all the new databases you create, simply modify the model database.
msdb Database – Used by the SQL Server Agent service.
tempdb Database – Is a workspace used for holding temporary information.