DEFINITION: The Windows
9x/NT/2000/ME/XP Registry is a complex, unified, system wide, continually
referenced during operation database, used for centrally storing, locating,
editing and administering system, hardware, software and user configuration
information, following a hierarchical structure.

It was introduced to replace the text/ASCII based MS -DOS
configuration (.BAT, .SYS) and MS Windows initialization (.INI) files.

Structure of Registry in windows 9X is Different from that of
Windows NT,2000 and XP.

Windows 95/98/ME :In these operating systems Registry is
stored in these 5 files, with the Hidden, Read-only attributes for
write-protection purposes, usually located in the %WinDir% folder (default is
C:\Windows) .

• SYSTEM.DAT = stores persistent
  hardware and software settings related to the system it resides on,
  contained in the (HKEY_CLASSES_ROOT = Windows 95 and 98 only) and
  HKEY_LOCAL_MACHINE Hive keys.
• USER.DAT = stores user specific
  and software settings contained in the HKEY_CURRENT_USER Hive key. If more
  than one user, then multiple user profiles enable each user to have their
  own separate USER.DAT file, located in %WinDir%\Profiles\%UserName%. When a
  user logs on, Windows OS (down)loads both USER.DAT files: the one from the
  local machine %WinDir% (global user settings), and the most recent one from
  the local machine %WinDir%\Profiles\%UserName%, or from the central (host)
  server if user profiles reside on a network (local user settings).
• CLASSES.DAT = stores persistent
  data contained in the HKEY_CLASSES_ROOT Hive key, found only on Windows ME.
• SYSTEM.DA0 and USER.DA0 =
  automatically created backups of SYSTEM.DAT and USER.DAT from the last
  successful Windows GUI startup, and found only on Windows 95

Windows NT/2000/XP :Registration
Database is contained in these 5 files located in the
%SystemRoot%\System32\Config folder (default is C:\Winnt\System32\Config for
Windows NT/2000 or C:\Windows\System32\Config for Windows XP):

• DEFAULT = stores the
  HKEY_USERS\.Default key.
• SAM = stores the
  HKEY_LOCAL_MACHINE\Sam key.
• SECURITY = stores the
  HKEY_LOCAL_MACHINE\Security key.
• SOFTWARE = stores the
  HKEY_LOCAL_MACHINE\Software key.
• SYSTEM = stores the
  HKEY_LOCAL_MACHINE\System key and the HKEY_CURRENT_CONFIG Hive key,

  these files located in the %SystemRoot%\Profiles\%UserName% folder:

   

• NTUSER.DAT and USRCLASS.DAT
  (Windows XP only) = store the HKEY_CURRENT_USER Hive key,

Editing Registry

Always make sure that you know what you are doing when
changing the registry or else just one little mistake can crash the whole
system. That’s why it’s always good to back it up!

To view the registry (or to back it up), you need to use the
Registry Editor tool. There are two versions of Registry Editor:

:To modify the Registry, you need to use a Registry Editor:

• Regedit.exe (Windows
  95/98/ME/NT/2000/XP) = located in %WinBootDir% (%SystemRoot%) has the most
  menu items and more choices for the menu items. You can search for keys and
  subkeys in the registry. 
• Regedt32.exe (Windows NT/2000/XP)
  = located in %SystemRoot%\System32,enables you to search for strings,
  values, keys, and subkeys. This feature is useful if you want to find
  specific data. 

Registry Structure

For ease of use, the Registry is divided into
five separate structures that represent the Registry database in its entirety.
These five groups are known as Keys, and are discussed below:

HKEY_CURRENT_USER

This registry key contains the configuration information for the user that is
currently logged in. The users folders, screen colors, and control panel
settings are stored here. This information is known as a User Profile.

HKEY_USERS

In windowsNT 3.5x, user profiles were stored locally (by default) in the
systemroot\system32\config directory. In NT4.0, they are stored in the
systemroot\profiles directory. User-Specific information is kept there, as well
as common, system wide user information.

HKEY_LOCAL_MACHINE

This key contains configuration information particular to the computer. This
information is stored in the systemroot\system32\config directory as persistent
operating system files, with the exception of the volatile hardware key.

HKEY_CLASSES_ROOT

The information stored here is used to open the correct application when a file
is opened by using Explorer and for Object Linking and Embedding. It is actually
a window that reflects information from the HKEY_LOCAL_MACHINE\Software subkey.

HKEY_CURRENT_CONFIG

The information contained in this key is to configure settings such as the
software and device drivers to load or the display resolution to use. This key
has a software and system subkeys, which keep track of configuration
information.

REG Files

.REG file, which can be in:

• plain text/ASCII format in
  Windows 95/98/ME and NT/2000/XP or
• binary format in Windows 2000/XP.Text .REG files can be easily viewed/created/edited by hand using any
  text/ASCII editor, like Notepad

Their purpose is to add, modify or delete Registry (Sub)Keys
and/or Values.

Writing .Reg Files

1.) Header line: this FIRST line is mandatory. MUST
contain only these exact words (case sensitive = character capitalization
required!):

• REGEDIT4 = for Windows 95/98/ME
  and NT 4.0 or
• Windows Registry Editor Version 5.00
  = for Windows 2000/XP.This is the only way Windows OS can recognize, validate and run a .REG file.

2.) Empty (blank) line: this
second line is optional. Similar to inserting a carriage return (CR).

3.) Remarked (comment) line(s): optional. MUST
begin with a semicolon (;) which may be followed by a space (optional). May be
inserted anywhere in the .REG file, but NOT before the header, which MUST be
present as FIRST line.

4.)(Sub)Key line: MUST be preceded and
terminated by square parenthesis ([]). (Sub)Key name MUST start with the Hive
Key name (left end) and MUST contain entire Subkey pathway leading to the
current Subkey name (right end). Consecutive (Sub)Key names MUST be separated by
SINGLE backslash marks (\).

(Sub)Key names not present in the Registry will be automatically created when
the REG file is merged into the Registry. Exception: new Hive (Root) Keys can be
created ONLY in Windows NT4/2000/XP, but NOT in Windows 95/98/ME.

5.)
Value line: MUST contain these elements in this
exact order:

• 
  Value name:
  MUST be preceded and terminated by quotation marks (“”).
• 
  Equal mark (=):
  separates Value name from Value type.
• 
  Value type:
  MUST be specified (Dword [REG_DWORD], Binary [REG_BINARY], etc) if Value
  type other than String [REG_SZ].
• 
  Colon mark (:):
  MUST exist if Value type other than String.
• 
  Value data: MUST be in the same format as defined by Value type:
  text/ASCII, Unicode/ANSI, (alpha)numeric (decimal, hexadecimal or binary)
  etc. MUST be preceded and terminated by quotation marks (“”)
  ONLY IF Value type is String.Value Data syntax

   

  • String Value [REG_SZ] (API Code 1):
    “ValueName”=”ValueData”Value Data is expressed here in Unicode or ANSI formats: simple
    text/ASCII, expanded or extended.
  • Dword Value [REG_DWORD] (API Code 4):
    “ValueName”=ValueType:ValueDataValue Data is expressed here in Double WORD (4 bytes = 32 bits) formats:
    decimal, hexadecimal or binary.
  • Large Binary (hex) Value (any Binary Value API Code):
    “ValueName”=ValueType(API
    Code):ValueData,ValueData,\

    ValueData,ValueData

    Large Values can span onto more than one line. Each
    line (except the last one) is terminated by a comma (,)
    followed by a SINGLE backslash mark (\).
    Consecutive lines are separated by carriage returns (CR).

Separators and delimiters used in REG files on path name
lines to separate drive letters, directory (folder) names and file names, or
used on command line parameters lines etc… MUST be typed as DOUBLE backslash
marks (\\).

6.) Empty (blank) line:
this LAST line is mandatory for proper operation. Similar to inserting a
carriage return (CR) at the end of file.

This is how a generic text/ASCII .REG
file looks like:

—–Begin cut ∓ paste here—–

REGEDIT4

; Comment line:

[HKEY_KEY_NAME\SubkeyName1\SubKeyName2]

; String Value format:

“ValueName”=”ValueData”

; Dword or Binary Value format:

“ValueName”=ValueType:ValueData

——End cut ∓ paste here——

Example of actual .REG file:

—–Begin cut ∓ paste here—–

REGEDIT4

; First Value below displays MS Windows version:

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion]

; String Value format:

“Version”=”Windows ME”

; Dword Value format:

“CacheWriteDelay”=dword:00000320

; Binary Value format:

“OldWinVer”=hex:00