What is the Registry?
The Registry is a database used to store
settings and options for the 32 bit versions of Microsoft Windows
including Windows 95, 98, ME and NT/2000. It contains information and
settings for all the hardware, software, users, and preferences of the
PC. Whenever a user makes changes to a Control Panel settings, or File
Associations, System Policies, or installed software, the changes are
reflected and stored in the Registry.
The physical files that
make up the registry are stored differently depending on your version
of Windows; under Windows 95 & 98 it is contained in two hidden
files in your Windows directory, called USER.DAT and SYSTEM.DAT, for
Windows Me there is an additional CLASSES.DAT file, while under Windows
NT/2000 the files are contained seperately in the
%SystemRoot%\System32\Config directory. You can not edit these files
directly, you must use a tool commonly known as a "Registry Editor" to
make any changes (using registry editors will be discussed later in the
article).
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.
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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