HKLM\SOFTWARE is the motherlode of software configuration information. Any configuration data an application or system component needs can be stored here; settings specific to an individual user belong in that user’s HKU\SOFTWARE key. For example, the SOFTWARE\Microsoft\Windows NT CurrentVersion\Winlogon key stores settings that apply to the winlogon program. These settings apply to all users on the machine, so they belong under HKLM. On the other hand, an individual user’s choices for which tools to use to view certain types of web content properly belong to that user, so they should go under HKCU (e.g., Software\Netscape\Netscape Navigator\Viewers).
This key is the root under which all the machinewide class definitions are registered. In NT, the HKCR root key displays data from this subkey alone. In Windows 2000, classes may also be registered under HKCU\Software\Classes, providing for class registration on a per-user bases. See HKCR\CLSID for details on the format of this key’s subkeys and values.
This key is the root location for parameters and settings for all Microsoft products installed on a machine. As you might expect, such a key covers a multitude of sins.
ActiveSetup is Microsoft’s name for its “new and improved” setup system. ActiveSetup records which components have been installed on a machine in the Installed Components subkey. Each installed component has its own class ID subkey under ...