What is the Registry?

A. A. Originally there were .ini files in Windows, however the problem with .ini files are many, e.g. size limitations, no standard layout, slow access, no network support etc. Windows 3.1 (yes Windows not Windows NT) had a registry which was stored in reg.dat and could be viewed using regedit.exe and was used for DDE, OLE and File Manager integration. In Windows NT the Registry is at the heart of NT and is where nearly all information is stored, and is split into a number of subtrees, each starting with HKEY_ to indicate that it is a handle that can be used by a program.

HKEY_LOCAL_MACHINE This contains information about the hardware configuration and installed software.
HKEY_CLASSES_ROOT This is just a link to HKEY_LOCAL_MACHINE\SOFTWARE\Classes and contains links between applications and file types as well as information about OLE.
HKEY_CURRENT_CONFIG Again this is a link to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Hardware Profiles\Current and contains information about the current configuration.
HKEY_CURRENT_USER This is a link to HKEY_USERS\<SID of User> and contains information about the currently logged on users such as environment, network connections, printers etc.
HKEY_USERS Contains information about actively loaded user profiles, including .default which is the default user profile.

Each of the subtrees has a number of keys, which in turn have a number of subkeys. Each key/subkey can have a number of values which has 3 parts

  • The name of the value, e.g. Wallpaper
  • The type of the value, e.g. REG_SZ (which is a text string)
  • The actual value of the value, e.g. "c:\winnt\savilltech.bmp"

To edit the registry there are two tools available, regedt32.exe and regedit.exe.Regedit.exe has better search facilities, but does not support all of the Windows NT registry value types. If you want to just have a look around the Registry:

  1. Start a registry editor (regedit.exe or regedt32.exe)
  2. In Regedt32.exe you can set the registry to read only mode which means you won't corrupt anything :-) (Options - Read Only Mode)
  3. Select the HKEY_USERS subkey
  4. Move to the .default - Control Panel - Desktop and you will see a number of values in the right hand pane.
  5. One of them is wallpaper and this is the background that is displayed before you logon.

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