System Databases in SQL Server
Master: Composed of system tables that keep track of server installation as a whole and all other databases that are eventually created. Master DB has system catalogs that keep info about disk space, file allocations and usage, configuration settings, endpoints, logins, etc.
Model: Template database. Gets cloned when a new database is created. Any changes that one would like be applied by default to a new database should be made here
Tempdb: Re-created every time SQL Server instance is restarted. Holds intermediate results created internally by SQL Server during query processing and sorting, maintaining row versions, etc. Recreated from the model database. Sizing and configuration of tempdb is critical for SQL Server performance.
Resource: Stores executable system objects such as stored system procedures and functions. Allows for very fast and safe upgrades.
MSDB: Used by the SQL Server Agent service and other companion services. Used for backups, replication tasks, Service Broker, supports jobs, alerts, log shipping, policies, database mail and recovery of damaged pages.
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