Let us continue our question of the day series with day twenty.

What is the DAC and how do I use it?

The DAC, or Dedicated Administrator Connection, is essentially a troubleshooting backdoor into a running instance of SQL Server.  The DAC is available through SSMS and the SQLCMD utility.  In SQL Server Management Studio choose New Query on the toolbar (assuming of course that you are not currently connected to any other DACs) as opposed to the Connect button in the Object Explorer, which will not work with DAC.  Once you are prompted for the connection enter ADMIN: in front of the Instance name\Server name (such as ADMIN:instance\server).  Then enter a sysadmin level credential.  If you are using the SQLCMD utility, then the command is sqlcmd -Sadmin:instance\server.

Enjoy!