Which Windows Registry root key stores machine-wide settings?

The Windows Registry root key that stores machine-wide settings is HKEY_LOCAL_MACHINE, usually abbreviated HKLM. It contains configuration for the computer itself rather than preferences belonging only to the currently signed-in user.

Important HKLM branches include SOFTWARE, which holds many application and Windows settings; SYSTEM, which covers hardware, drivers, services, and control sets; SECURITY; and SAM, the Security Accounts Manager database. These branches are loaded from registry hive files and are generally protected from ordinary users because changes can affect every account and service on the machine.

The usual contrast is HKEY_CURRENT_USER, or HKCU, which stores settings for one user profile. HKEY_USERS contains loaded user profiles, while HKEY_CLASSES_ROOT combines machine- and user-level class-registration information. Some software checks HKCU first and falls back to HKLM, and modern Windows can virtualize certain unsuitable writes to machine locations for compatibility.