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Configuration options take effect either:

• Immediately after setting the option and issuing the RECONFIGURE (or in some cases, RECONFIGURE WITH OVERRIDE) statement.
  -or-
  
• After performing the above actions and restarting the instance of SQL Server.
  

Options that require SQL Server to restart will initially show the changed value only in the value column. After restart, the new value will appear in both the value column and the value_in_use column.
Some options require a server restart before the new configuration value takes effect. If you set the new value and run sp_configure before restarting the server, the new value appears in the configuration options value column, but not in the value_in_use column. After restarting the server, the new value appears in the value_in_use column.
Self-configuring options are those that SQL Server adjusts according to the needs of the system. In most cases, this eliminates the need for setting the values manually. Examples include the min server memory and max server memory options and the user connections option.
The following table lists all available configuration options, the range of possible settings, and default values. Configuration options are marked with letter codes as follows:

• A= Advanced options, which should be changed only by an experienced database administrator or a certified SQL Server technician, and which require setting show advanced options to 1.
  
• RR = Options requiring a restart of the Database Engine.
  
• SC = Self-configuring options.