Because tempdb is so heavily used by the system, many system-wide performance optimizations are necessarily focused on making tempdb as efficient as possible. Tempdb is always recreated from when the SQL Server service is first started. This database is also used heavily by the database engine to serialize intermediate results and to hold other temporary data and objects that are generated during processing. The tempdb database holds user-created temporary database objects, such as temporary tables and temporary stored procedures. The tempdb database is considered a global resource that all connections and all users can access. Beginning with SQL Server 2005, the master database provides access to system objects through views, functions, and stored procedures that reference the read-only Resource database. Prior to SQL Server 2005 all system objects were stored in the master database.

This database records the initialization information for SQL Server, and an instance of SQL Server cannot start up if the master database is missing, corrupt, or otherwise unavailable. The master database stores metadata including references to all other databases on the instance. The master database records the server-wide configuration information for a SQL Server instance, including all logins and database engine configuration defaults. The Resource database is installed only with SQL Server 2005 and higher. Because the Resource database is read-only, it is only modified by the system when a SQL Server hotfix, service pack, or upgrade is installed on an instance. Interaction with the Resource database is indirect, through master database system views and functions that reference these objects. This system database is not displayed in the SQL Server Management Studio object explorer, so users may not be aware of it. The Resource database is a read-only database that contains all SQL Server system objects.

Resource ( SQL Server 2005 and higher only).

These system databases allow the database engine and administrative applications to properly manage the system: When you install Microsoft SQL Server, five system databases are automatically created on every SQL Server instance.

Ms sql master database