System databases are created by the SQL Server itself during the installation process. System databases are used by the SQL server to help manage other user databases and client execution sessions. SQL Server 2005 Express Edition uses 4 system databases:

* master - The brain of a SQL server - Stores server configuration, runtime information, and database metadata.

* model - An empty database model - Used to clone new databases.

* msdb - The background job scheduler - Used for background jobs and related tasks.

* tempdb - The temporary database - Used by the server as a scratch pad.