Search notes:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server

InstalledInstances

The value of InstalledInstances is string that contains the instance names (not instance IDs) of the installed instances on a server.
The values are stored in a REG_MULTI_SZ string, so each instance is stored in its own line.

See also

Compare with the other registry key HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\MSSQLServer.
SQL Server

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