The registry is a hierarchiral database that contains virtually all information about your computer's configuration. Under previous version of Windows, those settings were contained in files like config.sys, autoexec.bat, win.ini, system.ini, control.ini, and so on. From this you can understand how important the registry is.
The registry editor is a utility by the filename regedit.exe that allows you to see, search, modify and save the registry database of Windows. The registry editor does not validate the values you are writing: it allows any operation. Therefore the registry editor does not show any error messages. To launch the registry editor just run regedit.exe.
The registry is divided into keys and subkeys. Each key contains a value entry, each one has a name, a type or a class and the value itself. The name is a string that identifies the value to the key.
As you see in the registry editor, the registry is divided into five principal keys: there is no way to add or delete keys at this level. Only two of these keys are actually saved on the hard disk: HKEY_LOCAL_MACHINE and HKEY_USERS. The other are just branches of the main keys or are dynamcally created by Windows.
This key contains any hardware, applications and services information. Several hardware information is updated automatically while the computer is booting. The data stored in this key is shared with any user.
This key is an alias of the branch HKEY_LOCAL_MACHINE\Software\Classes and contains OLE, drag'n'drop, shortcut and file association information.
This key is also an alias. It contains a copy of the branch HKEY_LOCAL_MACHINE\Config, with the current computer configuration.
Some information stored in the registry changes frequently, so Windows maintains part of the registry in memory instead of on the hard disk. For example, it stores PnP information and computer performance.
This inportant key contains the sub-key. Default and another key for each user that has access to the computer. If there is just one user only default key exists. Each sub-key maintains the preferences of each user, likethe desktop colours, the fonts used, and also the settings of many programs.
It is an alias to current user of HKEY_USERS. If your computer is not configured for multi-users' usage,' it points to the subkey. Default of HKEY_USERS.