SQL Server System Databases

1.Master

The master database stores basic configuration information for the server. This includes information about the file locations of the user databases, as well as logon accounts, server configuration settings, and a number of other items such as linked servers and start up stored procedures.

Database ID of Master database is 1.

2.TempDB

The tempdb system databases is a shared temporary storage resource used by a number of features of SQL Server, and made available to all users.  Tempdb is used for temporary objects, worktables, online index operations, cursors, table variables, and the snapshot isolation version store, among other things.  It is recreated every time that the server is restarted, which means that no objects in tempdb are permanently stored. 

Database ID of  Tempdb database is 2.

3. Model 

The model database is a template database that is copied into a new database whenever it is created on the instance.

Database ID of Model database is 3.

4. MSDB

The msdb database is used to support a number of technologies within SQL Server, including the SQL Server Agent, SQL Server Management Studio, Database Mail, and Service Broker. It is also maintain the information about backup, SQL jobs.

Database ID of MSDB database is 4.

-- By Shivasagar V