Search notes:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server\instance name

Subkeys might be:

ClusterState
ConfigurationState
CPE
MSSQLServer
Providers
Security
Setup
SQLServerAgent
SQLServerSCP
UpgradeIncompleteState

TODO

What is, if at all, the relationship of this registry key to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\MSSQLServer

See also

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server\Instance Names