Why was "tantrum" trending last week?
The database used by Microsoft Windows 95 and later to store all sorts of configuration information such as which program should be used to open a .doc file, DLL registration information, application-specific settings and much more.
The Registry is stored in .dat files, one in the user's profile containing their per-user settings and one in the Windows directory containing settings that are global to all users. These are loaded into memory at login.
The loaded data appears as a tree with five main branches: HKEY_CLASSES_ROOT, HKEY_CURRENT_USER, HKEY_LOCAL_MACHINE, HKEY_USERS, HKEY_CURRENT_CONFIG. HKEY_CLASSES_ROOT defines file types and actions, HKEY_CURRENT_USER is an alias for one of the sub-trees of HKEY_USERS and contains user settings that override the global defaults in HKEY_LOCAL_MACHINE.
The branches of the tree are called "keys" and are identified by paths like HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion. Any node in the tree can have zero or more "values" which are actually bindings of a name and a value, e.g. "Logon User Name" = "Denis". The value can be of type string, binary, dword (long integer), multi-string value or expandable string value.
Windows includes a Registry Editor (regedit.exe).