The Structure of the Registry

The Registry has a hierarchal structure, although it looks complicated the structure is similar to the directory structure on your hard disk, with Regedit being similar to Windows Explorer.

Registry Structure [font_body]Each main branch (denoted by a folder icon in the Registry Editor, see left) is called a Hive, and Hives contains Keys. Each key can contain other keys (sometimes referred to as sub-keys), as well as Values. The values contain the actual information stored in the Registry. There are three types of values; String, Binary, and DWORD - the use of these depends upon the context.

There are six main branches, each containing a specific portion of the information stored in the Registry. They are as follows:

  • HKEY_CLASSES_ROOT - This branch contains all of your file association mappings to support the drag-and-drop feature, OLE information, Windows shortcuts, and core aspects of the Windows user interface.
  • HKEY_CURRENT_USER - This branch links to the section of HKEY_USERS appropriate for the user currently logged onto the PC and contains information such as logon names, desktop settings, and Start menu settings.
  • HKEY_LOCAL_MACHINE - This branch contains computer specific information about the type of hardware, software, and other preferences on a given PC, this information is used for all users who log onto this computer.
  • HKEY_USERS - This branch contains individual preferences for each user of the computer, each user is represented by a SID sub-key located under the main branch.
  • HKEY_CURRENT_CONFIG - This branch links to the section of HKEY_LOCAL_MACHINE appropriate for the current hardware configuration.
  • HKEY_DYN_DATA - This branch points to the part of HKEY_LOCAL_MACHINE, for use with the Plug-&-Play features of Windows, this section is dymanic and will change as devices are added and removed from the system.

Each registry value is stored as one of five main data types:

  • REG_BINARY - This type stores the value as raw binary data. Most hardware component information is stored as binary data, and can be displayed in an editor in hexadecimal format.
  • REG_DWORD - This type represents the data by a four byte number and is commonly used for boolean values, such as "0" is disabled and "1" is enabled. Additionally many parameters for device driver and services are this type, and can be displayed in REGEDT32 in binary, hexadecimal and decimal format, or in REGEDIT in hexadecimal and decimal format.
  • REG_EXPAND_SZ - This type is an expandable data string that is string containing a variable to be replaced when called by an application. For example, for the following value, the string "%SystemRoot%" will replaced by the actual location of the directory containing the Windows NT system files. (This type is only available using an advanced registry editor such as REGEDT32)
  • REG_MULTI_SZ - This type is a multiple string used to represent values that contain lists or multiple values, each entry is separated by a NULL character. (This type is only available using an advanced registry editor such as REGEDT32)
  • REG_SZ - This type is a standard string, used to represent human readable text values.
Other data types not available through the standard registry editors include:
  • REG_DWORD_LITTLE_ENDIAN - A 32-bit number in little-endian format.
  • REG_DWORD_BIG_ENDIAN - A 32-bit number in big-endian format.
  • REG_LINK - A Unicode symbolic link. Used internally; applications should not use this type.
  • REG_NONE - No defined value type.
  • REG_QWORD - A 64-bit number.
  • REG_QWORD_LITTLE_ENDIAN - A 64-bit number in little-endian format.
  • REG_RESOURCE_LIST - A device-driver resource list.

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