SQL Server related information from Windows registries
The Windows Registry is a hierarchical database that stores configuration settings and options on Microsoft Windows operating systems. It contains settings for low-level operating system components and for applications running on the platform that have opted to use the registry. The kernel, device drivers, services, SAM, user interface and third party applications can all make use of the registry. The registry also provides a means to access counters for profiling system performance.
See Wikipedia Article Windows Registry.
To View SQL Server related registries.
Go to Run and type regedit
HKLU=>Software=>Microsoft=>Microsoft SQL Server
To find valuable information about edition, version, patch label etc. Traverse as below pic
To Change Default authentication mode 1-window authentication 2-SQL server Authentication
Edit Login Mode registry value.
Value= 1 for Window Authentication
Value=2 for SQL server Authentication
Restart SQL server and agent services your default SQL server authentication mode has been changed. You can change for each instance of SQL server.
Note: Serious problems might occur if you modify the registry incorrectly. So do not modify any registry if you do not understand it.
However you can achieve same using xp_instance_regwrite stored procedure to edit registries.as
The below query is used to change authentication mode from mixed to Windows only.
EXEC xp_instance_regwrite
N'HKEY_LOCAL_MACHINE',
N'Software\Microsoft\MSSQLServer\MSSQLServer',
N'LoginMode',
REG_DWORD,
1;
The below query is used to change authentication mode from windows only to Mixed back.
EXEC xp_instance_regwrite
N'HKEY_LOCAL_MACHINE',
N'Software\Microsoft\MSSQLServer\MSSQLServer',
N'LoginMode',
REG_DWORD,
2;
Each time you execute query,restart the server and check.
To find installed instances on current machine, traverse as below pic
