The Windows Registry is a hierarchical database that stores configuration settings and options on Microsoft Windows
Microsoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
s. It contains settings for low-level operating system components as well as the applications running on the platform: the kernel
Kernel (computing)
In computing, the kernel is the main component of most computer operating systems; it is a bridge between applications and the actual data processing done at the hardware level. The kernel's responsibilities include managing the system's resources...
On Microsoft Windows operating systems, a Windows service is a long-running executable that performs specific functions and which is designed not to require user intervention. Windows services can be configured to start when the operating system is booted and run in the background as long as...
In computing, a graphical user interface is a type of user interface that allows users to interact with electronic devices with images rather than text commands. GUIs can be used in computers, hand-held devices such as MP3 players, portable media players or gaming devices, household appliances and...
and third party applications all make use of the registry. The registry also provides a means to access counters
Instrumentation (computer programming)
In context of computer programming, instrumentation refers to an ability to monitor or measure the level of a product's performance, to diagnose errors and to write trace information. Programmers implement instrumentation in the form of code instructions that monitor specific components in a system...
for profiling system performance.
When first introduced with Windows 3.1, the Windows registry's primary purpose was to store configuration information for COM
Component Object Model
Component Object Model is a binary-interface standard for software componentry introduced by Microsoft in 1993. It is used to enable interprocess communication and dynamic object creation in a large range of programming languages...
-based components. With the introduction of Windows 95 and Windows NT, its use was extended to tidy up the profusion of per-program INI files that had previously been used to store configuration settings for Windows programs.
Rationale
.INI files stored each program's settings into a text file, often located in a shared location that did not allow for user-specific settings in a multi-user scenario. By contrast, the Windows registry stores all application settings in one central repository and in a standardized form. This offers several advantages over INI files. Since file parsing is done much more efficiently with a binary format, it may be read from or written to more quickly than an INI file. As well, strongly typed data can be stored in the registry, as opposed to the text information stored in INI files. This is a benefit when editing keys manually using regedit, the built-in Windows registry editor. Because user-based registry settings are loaded from a user-specific path rather than from a read-only system location, the registry allows multiple users to share the same machine, and also allows programs to work for less privileged users. Backup and restoration is also simplified as the registry can be accessed over a network connection for remote management/support, including from scripts, using the standard set of APIs, as long as the Remote Registry service
Windows Service
On Microsoft Windows operating systems, a Windows service is a long-running executable that performs specific functions and which is designed not to require user intervention. Windows services can be configured to start when the operating system is booted and run in the background as long as...
is running and firewall rules permit this.
The registry has features that improve system integrity, as the registry is constructed as a database and offers database-like features such as atomic updates. If two processes attempt to update the same registry value at the same time, one process's change will precede the other's and the overall consistency of the data will be maintained. Where changes are made to INI files, such race conditions
Race condition
A race condition or race hazard is a flaw in an electronic system or process whereby the output or result of the process is unexpectedly and critically dependent on the sequence or timing of other events...
can result in inconsistent data which doesn't match either attempted update. Windows Vista and later operating systems provide transactional updates to the registry by means of the Kernel Transaction Manager
Kernel Transaction Manager
Kernel Transaction Manager is a component of the Windows operating system kernel in Windows Vista and Windows Server 2008 that enables applications to use atomic transactions on resources by making them available as kernel objects...
, extending the atomicity guarantees across multiple key and/or value changes, with traditional commit-abort semantics. (Note however that NTFS
NTFS
NTFS is the standard file system of Windows NT, including its later versions Windows 2000, Windows XP, Windows Server 2003, Windows Server 2008, Windows Vista, and Windows 7....
provides such support for the file system as well, so the same guarantees could, in theory, be obtained with traditional configuration files.)
Criticism
While offering improvements over application-specific .INI files, the organization and implementation of the registry also has potential problems:
Installers and uninstallers become more complex when applications rely on Registry configuration settings that need to be created by installation applications, because these Registry settings cannot be transferred by copying the application files that comprise the application. Use of the Registry by non-COM based applications is optional; .NET applications use a configuration file instead of the Registry. Some other operating systems (e.g., Apple's Mac OS X
Mac OS X
Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...
and preceding iterations) also support installation through simple file copy.
Because information required for loading device drivers is stored in the registry, a damaged System registry can stop device drivers from loading, leading to loss of functionality or inability of the Windows system to boot, and forcing a user to utilize the last known configuration in order to successfully boot, if available.
The parts of the registry may have to be kept in sync with the file system (e.g., deleting a COM
Component Object Model
Component Object Model is a binary-interface standard for software componentry introduced by Microsoft in 1993. It is used to enable interprocess communication and dynamic object creation in a large range of programming languages...
-based application from the file system rather than uninstalling it may leave associated configuration items entries in the registry if the application is legacy and does not use side-by-side registry-free configuration.)
Applications that make use of the registry to store and retrieve their settings may be unsuitable for use on portable devices used to carry applications from one system to another. Similarly, it is often not possible to copy installed applications that use the Registry to another computer. This means that software usually has to be reinstalled from original media after a computer upgrade or rebuild, or each of COM components manually re-registered. Registration-free COM addresses this problem and Application virtualization
Application Virtualization
Application virtualization is an umbrella term that describes software technologies that improve portability, manageability and compatibility of applications by encapsulating them from the underlying operating system on which they are executed. A fully virtualized application is not installed in...
attempts to work around it.
The centralized nature of the registry creates interdependencies between applications and system components that undermine the engineering principle of modular design
Modular design
Modular design, or "modularity in design" is an approach that subdivides a system into smaller parts that can be independently created and then used in different systems to drive multiple functionalities...
. Any process with sufficient privileges can delete or modify configuration data associated with other programs or system components and thereby potentially cause them to fail.
Keys and values
The registry contains two basic elements: keys and values.
Registry keys are similar to folders — in addition to values, each key can contain subkeys, which may contain further subkeys, and so on. Keys are referenced with a syntax similar to Windows' path names, using backslashes to indicate levels of hierarchy. Each subkey has a mandatory name, which is a non-empty string that cannot contain any backslash, and whose letter case is insignificant
Case sensitivity
Text sometimes exhibits case sensitivity; that is, words can differ in meaning based on differing use of uppercase and lowercase letters. Words with capital letters do not always have the same meaning when written with lowercase letters....
.
The hierarchy of registry keys can only be accessed from a known root key handle (which is anonymous but whose effective value is a constant numeric handle) that is mapped to the content of a registry key preloaded by the kernel from a stored "hive", or to the content of a subkey within another root key, or mapped to a registered service or DLL that provide access to its contained subkeys and values.
E.g. HKEY_LOCAL_MACHINE\Software\Microsoft\Windows refers to the subkey "Windows" of the subkey "Microsoft" of the subkey "Software" of the HKEY_LOCAL_MACHINE root key.
There are seven predefined root keys, traditionally named according to their constant handles defined in the Win32 API, or by synonymous abbreviations (depending on applications):
HKEY_LOCAL_MACHINE or HKLM
HKEY_CURRENT_CONFIG or HKCC (only in Windows 9x/Me and NT-based versions of Windows)
HKEY_CLASSES_ROOT or HKCR
HKEY_CURRENT_USER or HKCU
HKEY_USERS or HKU
HKEY_PERFORMANCE_DATA (only in NT-based versions of Windows, but invisible in the Windows Registry Editor)
HKEY_DYN_DATA (only in Windows 9x/Me, and visible in the Windows Registry Editor)
Like other files and services in Windows, all registry keys may be restricted by access control list
Access control list
An access control list , with respect to a computer file system, is a list of permissions attached to an object. An ACL specifies which users or system processes are granted access to objects, as well as what operations are allowed on given objects. Each entry in a typical ACL specifies a subject...
s (ACLs), depending on user privileges, or on security tokens acquired by applications, or on system security policies enforced by the system (these restrictions may be predefined by the system itself, and configured by local system administrators or by domain administrators). Different users, programs, services or remote systems may only see some parts of the hierarchy or distinct hierarchies from the same root keys.
Registry values are name/data pairs stored within keys. Registry values are referenced separately from registry keys. Each registry value stored in a registry key has a unique name whose letter case is not significant. The Windows API
Windows API
The Windows API, informally WinAPI, is Microsoft's core set of application programming interfaces available in the Microsoft Windows operating systems. It was formerly called the Win32 API; however, the name "Windows API" more accurately reflects its roots in 16-bit Windows and its support on...
functions that query and manipulate registry values take value names separately from the key path and/or handle that identifies the parent key. Registry values may contain backslashes in their name but doing so makes them difficult to distinguish from their key paths when using some legacy Windows Registry API functions (whose usage is deprecated in Win32).
The terminology is somewhat misleading, as each registry key is similar to an associative array
Associative array
In computer science, an associative array is an abstract data type composed of a collection of pairs, such that each possible key appears at most once in the collection....
, where standard terminology would refer to the name part of each registry value as a "key". The terms are a holdout from the 16-bit registry in Windows 3, in which registry keys could not contain arbitrary name/data pairs, but rather contained only one unnamed value (which had to be a string). In this sense, the entire registry was like a single associative array where the registry keys (in both the registry sense and dictionary sense) formed a hierarchy, and the registry values were all strings. When the 32-bit registry was created, so was the additional capability of creating multiple named values per key, and the meanings of the names were somewhat distorted. For compatibility with the previous behavior, each registry key may have a "default" value, whose name is the empty string.
Each value can store arbitrary data with variable length and encoding, but which is associated with a symbolic type (defined as a numeric constant) defining how to parse this data. The standard types are :
List of standard registry value types
Type ID
Symbolic type name
Meaning and encoding of the data stored in the registry value
In formal languages, which are used in mathematical logic and theoretical computer science, a string is a finite sequence of symbols that are chosen from a set or alphabet....
value, normally stored and exposed in UTF-16LE (when using the Unicode version of Win32 API functions), usually terminated by a null character
2
REG_EXPAND_SZ
An "expandable" string value that can contain environment variables, normally stored and exposed in UTF-16LE, usually terminated by a null character
In computing, signedness is a property of data types representing numbers in computer programs. A numeric variable is signed if it can represent both positive and negative numbers, and unsigned if it can only represent non-negative numbers .As signed numbers can represent negative numbers, they...
The integers are formed by the natural numbers together with the negatives of the non-zero natural numbers .They are known as Positive and Negative Integers respectively...
(numbers between 0 and 4,294,967,295 [232 – 1]) (little-endian
Endianness
In computing, the term endian or endianness refers to the ordering of individually addressable sub-components within the representation of a larger data item as stored in external memory . Each sub-component in the representation has a unique degree of significance, like the place value of digits...
In computing, signedness is a property of data types representing numbers in computer programs. A numeric variable is signed if it can represent both positive and negative numbers, and unsigned if it can only represent non-negative numbers .As signed numbers can represent negative numbers, they...
The integers are formed by the natural numbers together with the negatives of the non-zero natural numbers .They are known as Positive and Negative Integers respectively...
(numbers between 0 and 4,294,967,295 [232 – 1]) (big-endian
Endianness
In computing, the term endian or endianness refers to the ordering of individually addressable sub-components within the representation of a larger data item as stored in external memory . Each sub-component in the representation has a unique degree of significance, like the place value of digits...
)
6
REG_LINK
A symbolic link (UNICODE) to another registry key, specifying a root key and the path to the target key
7
REG_MULTI_SZ
A multi-string value, which is an ordered list of non-empty strings
String (computer science)
In formal languages, which are used in mathematical logic and theoretical computer science, a string is a finite sequence of symbols that are chosen from a set or alphabet....
, normally stored and exposed in UTF-16LE, each one terminated by a null character, the list being normally terminated by a second null character.
8
REG_RESOURCE_LIST
A resource list (used by the Plug-n-Play hardware enumeration and configuration)
9
REG_FULL_RESOURCE_DESCRIPTOR
A resource descriptor (used by the Plug-n-Play hardware enumeration and configuration)
10
REG_RESOURCE_REQUIREMENTS_LIST
A resource requirements list (used by the Plug-n-Play hardware enumeration and configuration)
11
REG_QWORD / REG_QWORD_LITTLE_ENDIAN
A QWORD value, a 64-bit integer (either big- or little-endian, or unspecified) (Introduced in Windows 2000
Windows 2000
Windows 2000 is a line of operating systems produced by Microsoft for use on personal computers, business desktops, laptops, and servers. Windows 2000 was released to manufacturing on 15 December 1999 and launched to retail on 17 February 2000. It is the successor to Windows NT 4.0, and is the...
)
Hives
The Registry comprises a number of logical sections, or "hives" (the word hive constitutes an in-joke
In-joke
An in-joke, also known as an inside joke or in joke, is a joke whose humour is clear only to people who are in a particular social group, occupation, or other community of common understanding...
The Windows API, informally WinAPI, is Microsoft's core set of application programming interfaces available in the Microsoft Windows operating systems. It was formerly called the Win32 API; however, the name "Windows API" more accurately reflects its roots in 16-bit Windows and its support on...
An application programming interface is a source code based specification intended to be used as an interface by software components to communicate with each other...
definitions, which all begin "HKEY". They are frequently abbreviated to a three- or four-letter short name starting with "HK" (e.g. HKCU and HKLM). Technically, they are predefined handles (with known constant values) to specific keys that are either maintained in memory, or stored in hive files stored in the local filesystem and loaded by the system kernel at boot time and then shared (with various access rights) between all processes running on the local system, or loaded and mapped in all processes started in a user session when the user logs on the system.
The HKEY_LOCAL_MACHINE (local machine-specific configuration data) and HKEY_CURRENT_USER (user-specific configuration data) nodes have a similar structure to each other; user applications typically look up their settings by first checking for them in "HKEY_CURRENT_USER\Software\Vendor's name\Application's name\Version\Setting name", and if the setting is not found, look instead in the same location under the HKEY_LOCAL_MACHINE key. However, the converse may apply for administrator-enforced policy
Group Policy
Group Policy is a feature of the Microsoft Windows NT family of operating systems. Group Policy is a set of rules that control the working environment of user accounts and computer accounts. Group Policy provides the centralized management and configuration of operating systems, applications, and...
Windows Hardware Quality Labs testing or WHQL Testing is Microsoft's testing process which involves running a series of tests on third-party hardware or software, and then submitting the log files from these tests to Microsoft for review...
has specific requirements for where different types of user data may be stored, and that the concept of least privilege
Principle of least privilege
In information security, computer science, and other fields, the principle of least privilege, also known as the principle of minimal privilege or just least privilege, requires that in a particular abstraction layer of a computing environment, every module must be able to access only the...
be followed so that administrator-level access is not required to use an application.When applications fail to execute because they request more privileges than they require (and are denied those privileges), this is known as a limited user application (LUA) bug.
HKEY_LOCAL_MACHINE (HKLM)
Abbreviated HKLM, HKEY_LOCAL_MACHINE stores settings that are specific to the local computer.
The key located by HKLM is actually not stored on disk, but maintained in memory by the system kernel in order to map there all other subkeys. Applications cannot create any additional subkeys. On NT-based versions of Windows, this key contains four subkeys, "SAM", "SECURITY", "SYSTEM", and "SOFTWARE", that are loaded at boot time within their respective files located in the %SystemRoot%\System32\config folder. A fifth subkey, "HARDWARE", is volatile and is created dynamically, and as such is not stored in a file (it exposes a view of all the currently detected Plug-and-Play devices). On Windows Vista and above, a sixth subkey is mapped in memory by the kernel and populated from boot configuration data (BCD).
The "HKLM\SAM" key usually appears as empty for most users (unless they are granted access by administrators of the local system or administrators of domains managing the local system). It is used to reference all "Security Accounts Manager" (SAM) databases for all domains into which the local system has been administratively authorized or configured (including the local domain of the running system, whose SAM database is stored a subkey also named "SAM": other subkeys will be created as needed, one for each supplementary domain). Each SAM database contains all builtin accounts (mostly group aliases) and configured accounts (users, groups and their aliases, including guest accounts and administrator accounts) created and configured on the respective domain, for each account in that domain, it notably contains the user name which can be used to log on that domain, the internal unique user identifier in the domain, a cryptographic hash
Cryptographic hash function
A cryptographic hash function is a deterministic procedure that takes an arbitrary block of data and returns a fixed-size bit string, the hash value, such that an accidental or intentional change to the data will change the hash value...
An authentication protocol is a type of cryptographic protocol with the purpose of authenticating entities wishing to communicate securely.There are many different authentication protocols such as:* AKA* CAVE-based_authentication...
, the location of storage of their user registry hive, various status flags (for example if the account can be enumerated and be visible in the logon prompt screen), and the list of domains (including the local domain) into which the account was configured.
The "HKLM\SECURITY" key usually appears empty for most users (unless they are granted access by users with administrative privileges) and is linked to the Security database of the domain into which the current user is logged on (if the user is logged on the local system domain, this key will be linked to the registry hive stored by the local machine and managed by local system administrators or by the builtin "System" account and Windows installers). The kernel will access it to read and enforce the security policy applicable to the current user and all applications or operations executed by this user. It also contains a "SAM" subkey which is dynamically linked to the SAM database of the domain onto which the current user is logged on.
The "HKLM\SYSTEM" key is normally only writable by users with administrative privileges on the local system. It contains information about the Windows system setup, data for the secure random number generator (RNG), the list of currently mounted devices containing a filesystem, several numbered "HKLM\SYSTEM\Control Sets" containing alternative configurations for system hardware drivers and services running on the local system (including the currently used one and a backup), a "HKLM\SYSTEM\Select" subkey containing the status of these Control Sets, and a "HKLM\SYSTEM\CurrentControlSet" which is dynamically linked at boot time to the Control Set which is currently used on the local system. Each configured Control Set contains:
an "Enum" subkey enumerating all known Plug-and-Play devices and associating them with installed system drivers (and storing the device-specific configurations of these drivers),
a "Services" subkey listing all installed system drivers (with non device-specific configuration, and the enumeration of devices for which they are instanciated) and all programs running as services (how and when they can be automatically started),
a "Control" subkey organizing the various hardware drivers and programs running as services and all other system-wide configuration,
a "Hardware Profiles" subkey enumerating the various profiles that have been tuned (each one with "System" or "Software" settings used to modify the default profile, either in system drivers and services or in the applications) as well as the "Hardware Profiles\Current" subkey which is dynamically linked to one of these profiles.
The "HKLM\SOFTWARE" subkey contains software and Windows settings (in the default hardware profile). It is mostly modified by application and system installers. It is organized by software vendor (with a subkey for each), but also contains a "Windows" subkey for some settings of the Windows user interface, a "Classes" subkey containing all registered associations from file extensions, MIME types, Object Classes IDs and interfaces IDs (for OLE, COM/DCOM and ActiveX), to the installed applications or DLLs that may be handling these types on the local machine (however these associations are configurable for each user, see below), and a "Policies" subkey (also organized by vendor) for enforcing general usage policies on applications and system services (including the central certificates store used for authentifying, authorizing or disallowing remote systems or services running outside of the local network domain).
The "HKLM\SOFTWARE\Wow6432Node" key is used by 32-bit applications on a 64-bit Windows OS, and is equivalent but separate to "HKLM\SOFTWARE". The key path is transparently presented to 32-bit applications by WoW64
WoW64
WoW64 is a subsystem of the Windows operating system that is capable of running 32-bit applications and is included on all 64-bit versions of Windows—including Windows XP Professional x64 Edition, IA-64 and x64 versions of Windows Server 2003, as well as 64-bit versions of Windows Vista, Windows...
as HKLM\SOFTWARE (in a similar way that 32-bit applications see %SystemRoot%\Syswow64 as %SystemRoot%\System32)
HKEY_CURRENT_CONFIG (HKCC)
Abbreviated HKCC, HKEY_CURRENT_CONFIG contains information gathered at runtime; information stored in this key is not permanently stored on disk, but rather regenerated at boot time. It is a handle to the key "HKEY_LOCAL_MACHINE\System\CurrentControlSet\Hardware Profiles\Current", which is initially empty but populated at boot time by loading one of the other subkeys stored in "HKEY_LOCAL_MACHINE\System\CurrentControlSet\Hardware Profiles".
HKEY_CLASSES_ROOT (HKCR)
Abbreviated HKCR, HKEY_CLASSES_ROOT contains information about registered applications, such as file association
File association
A file association associates a file with an application capable of opening that file. More commonly, a file association associates a class of files with a corresponding application .-Associations and verbs:A single file extension may have several associations for performing various actions, also...
Object Linking and Embedding is a technology developed by Microsoft that allows embedding and linking to documents and other objects. For developers, it brought OLE Control eXtension , a way to develop and use custom user interface elements...
Object Class IDs, tying them to the applications used to handle these items. On Windows 2000
Windows 2000
Windows 2000 is a line of operating systems produced by Microsoft for use on personal computers, business desktops, laptops, and servers. Windows 2000 was released to manufacturing on 15 December 1999 and launched to retail on 17 February 2000. It is the successor to Windows NT 4.0, and is the...
and above, HKCR is a compilation of user-based HKCU\Software\Classes and machine-based HKLM\Software\Classes. If a given value exists in both of the subkeys above, the one in HKCU\Software\Classes takes precedence. The design allows for either machine- or user-specific registration of COM
Component Object Model
Component Object Model is a binary-interface standard for software componentry introduced by Microsoft in 1993. It is used to enable interprocess communication and dynamic object creation in a large range of programming languages...
objects. The user-specific classes hive, unlike the HKCU hive, does not form part of a roaming user profile.
HKEY_USERS (HKU)
Abbreviated HKU, HKEY_USERS contains subkeys corresponding to the HKEY_CURRENT_USER keys for each user profile actively loaded on the machine, though user hives are usually only loaded for currently logged-in users.
HKEY_CURRENT_USER (HKCU)
Abbreviated HKCU, HKEY_CURRENT_USER stores settings that are specific to the currently logged-in user. The HKCU key is a link to the subkey of HKEY_USERS that corresponds to the user; the same information is accessible in both locations. On Windows NT-based systems, each user's settings are stored in their own files called NTUSER.DAT and USRCLASS.DAT inside their own Documents and Settings subfolder (or their own Users sub folder in Windows Vista and above). Settings in this hive follow users with a roaming profile
Roaming user profile
A roaming user profile is a concept in the Microsoft Windows NT family of operating systems that allows a user with a computer joined to a Windows Server domain to log on to any computer on the same network and access their documents and have a consistent desktop experience, such as applications...
from machine to machine.
HKEY_PERFORMANCE_DATA
This key provides runtime information into performance data provided by either the NT kernel itself, or running system drivers, programs and services that provide performance data. This key is not stored in any hive and not displayed in the Registry Editor, but it is visible through the registry functions in the Windows API, or in a simplified view via the Performance tab of the Task Manager (only for a few performance data on the local system) or via more advanced control panels (such as the Performances Monitor or the Performances Analyzer which allows collecting and logging these data, including from remote systems).
HKEY_DYN_DATA
This key is used only on Windows 95, Windows 98 and Windows Me. It contains information about hardware devices, including Plug and Play and network performance statistics. The information in this hive is also not stored on the hard drive. The Plug and Play information is gathered and configured at startup and is stored in memory.
Manual editing
The Windows registry can be edited manually using programs such as regedit.exe and on older versions of Windows, regedt32.exe, although these tools do not expose some of registry's metadata such as the last modified date. They also implement workarounds in code that allow Registry keys to be renamed, as the underlying APIs do not support this capability.
As a careless change could cause irreversible damage, a backup of the registry before editing is recommended by Microsoft.
A simple implementation of the current registry tool appeared in Windows 3.x
Windows 3.1x
Windows 3.1x is a series of 16-bit operating systems produced by Microsoft for use on personal computers. The series began with Windows 3.1, which was first sold during March 1992 as a successor to Windows 3.0...
, called the "Registration Info Editor" or "Registration Editor". This was basically just a database
Database
A database is an organized collection of data for one or more purposes, usually in digital form. The data are typically organized to model relevant aspects of reality , in a way that supports processes requiring this information...
Object Linking and Embedding is a technology developed by Microsoft that allows embedding and linking to documents and other objects. For developers, it brought OLE Control eXtension , a way to develop and use custom user interface elements...
Windows 9x is a generic term referring to a series of Microsoft Windows computer operating systems produced since 1995, which were based on the original and later modified Windows 95 kernel...
operating systems included REGEDIT.EXE which could be used in Windows and also in real mode
Real mode
Real mode, also called real address mode, is an operating mode of 80286 and later x86-compatible CPUs. Real mode is characterized by a 20 bit segmented memory address space and unlimited direct software access to all memory, I/O addresses and peripheral hardware...
MS-DOS is an operating system for x86-based personal computers. It was the most commonly used member of the DOS family of operating systems, and was the main operating system for IBM PC compatible personal computers during the 1980s to the mid 1990s, until it was gradually superseded by operating...
Windows NT is a family of operating systems produced by Microsoft, the first version of which was released in July 1993. It was a powerful high-level-language-based, processor-independent, multiprocessing, multiuser operating system with features comparable to Unix. It was intended to complement...
introduced permissions for Registry editing. Windows NT 4.0 and Windows 2000
Windows 2000
Windows 2000 is a line of operating systems produced by Microsoft for use on personal computers, business desktops, laptops, and servers. Windows 2000 was released to manufacturing on 15 December 1999 and launched to retail on 17 February 2000. It is the successor to Windows NT 4.0, and is the...
were distributed with both the Windows 9x REGEDIT.EXE program and Windows NT 3.x's REGEDT32.EXE program. There were several differences between the two editors on these platforms:
REGEDIT.EXE had a left-side tree view that begins at "My Computer" and lists all loaded hives. REGEDT32.EXE had a left-side tree view, but each hive had its own window, so the tree displays only keys.
REGEDIT.EXE represented the three components of a value (its name, type, and data) as separate columns of a table. REGEDT32.EXE represented them as a list of strings.
REGEDIT.EXE supported right-clicking of entries in a tree view to adjust properties and other settings. REGEDT32.EXE required all actions to be performed from the top menu bar.
REGEDIT.EXE supported searching for key names, values, or data throughout the entire registry, whereas REGEDT32.EXE only supported searching for key names in one hive at a time.
Earlier versions of REGEDIT.EXE did not support editing permissions. Therefore, on those early versions, only REGEDT32.EXE could access the full functionality of an NT registry. REGEDIT.EXE in Windows XP and above supports editing permissions.
REGEDIT.EXE only supported string (REG_SZ), binary (REG_BINARY), and DWORD (REG_DWORD) values. REGEDT32.EXE supported those, plus expandable string (REG_EXPAND_SZ) and multi-string (REG_MULTI_SZ). Attempting to edit unsupported key types with REGEDIT.EXE on Windows 2000 or Windows NT 4.0 would result in irreversible conversion to a supported type.
Windows XP is an operating system produced by Microsoft for use on personal computers, including home and business desktops, laptops and media centers. First released to computer manufacturers on August 24, 2001, it is the second most popular version of Windows, based on installed user base...
was the first system to integrate these two programs into one, adopting the old REGEDIT.EXE interface and adding the REGEDT32.EXE functionality. The differences listed above are not applicable on Windows XP and newer systems; REGEDIT.EXE is the improved editor, and REGEDT32.EXE is deprecated. On Windows XP and above, the Registry Editor also supports multiple instances if the -m switch is specified.
The Registry Editor allows users to perform the following functions:
Creating, manipulating, renaming and deleting registry keys, subkeys, values and value data
Importing and exporting .REG files, exporting data in the binary hive format
Loading, manipulating and unloading registry hive format files (Windows NT-based systems only)
An access control list , with respect to a computer file system, is a list of permissions attached to an object. An ACL specifies which users or system processes are granted access to objects, as well as what operations are allowed on given objects. Each entry in a typical ACL specifies a subject...
(Windows NT-based systems only)
Bookmarking user-selected registry keys as Favorites
Finding particular strings in key names, value names and value data
Remotely editing the registry on another networked computer
It is also possible to edit the registry under Linux
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
.REG files (also known as Registration entries) are text-based human-readable files for exporting and importing portions of the registry. On Windows 2000
Windows 2000
Windows 2000 is a line of operating systems produced by Microsoft for use on personal computers, business desktops, laptops, and servers. Windows 2000 was released to manufacturing on 15 December 1999 and launched to retail on 17 February 2000. It is the successor to Windows NT 4.0, and is the...
and later NT-based operating systems, they contain the string Windows Registry Editor Version 5.00 at the beginning and are Unicode
Unicode
Unicode is a computing industry standard for the consistent encoding, representation and handling of text expressed in most of the world's writing systems...
Windows 9x is a generic term referring to a series of Microsoft Windows computer operating systems produced since 1995, which were based on the original and later modified Windows 95 kernel...
and NT 4.0 systems, they contain the string REGEDIT4 and are ANSI
Windows-1252
Windows-1252 or CP-1252 is a character encoding of the Latin alphabet, used by default in the legacy components of Microsoft Windows in English and some other Western languages. It is one version within the group of Windows code pages...
-based. Windows 9x format .REG files are compatible with Windows 2000 and later NT-based systems. The Registry Editor on Windows on these systems also supports exporting .REG files in Windows 9x/NT format. Data is stored in .REG files in the following syntax:
[\\]
"Value Name"=:
The Default Value of a key can be edited by using @ instead of "Value Name":
[\\]
@=:
String values do not require a (see example), but backslashes ("\") need to be written as a double-backslash ("\\").
For example, to add the values "Value A", "Value B", "Value C", "Value D", "Value E", "Value F", "Value G", "Value H" and "Value I" to the HKLM\SOFTWARE\Microsoft key,
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft]
"Value A"=""
"Value B"=hex:
"Value C"=dword:
"Value D"=hex(7):
"Value E"=hex(2):
"Value F"=hex(b):
"Value G"=hex(4):
"Value H"=hex(5):
"Value I"=hex(0):
Data from .REG files can be added/merged with the registry by double-clicking these files or using the /s switch in the command line. .REG files can also be used to remove registry data.
To remove a key (and all subkeys, values and data), the key name must be preceded by a minus sign ("-").
For example, to remove the HKLM\SOFTWARE\Microsoft key (and all subkeys, values and data),
[-HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft]
To remove a value (and its data), the values to be removed must have a minus sign ("-") after the equal sign ("=").
For example, to remove only the "Value A" and "Value B" values (and their data) from the HKLM\SOFTWARE\Microsoft key,
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft]
"Value A"=-
"Value B"=-
To remove only the (Default) value of the key HKLM\SOFTWARE\Microsoft (and its data),
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft]
@=-
Command line editing
The registry can be manipulated in a number of ways from the command line. The Reg.exe and RegIni.exe utility tools are included in Windows XP
Windows XP
Windows XP is an operating system produced by Microsoft for use on personal computers, including home and business desktops, laptops and media centers. First released to computer manufacturers on August 24, 2001, it is the second most popular version of Windows, based on installed user base...
and later versions of Windows. Alternative locations for legacy versions of Windows include the Resource Kit CDs or the original Installation CD of Windows.
Also, a .REG file can be imported from the command line with the following command:
RegEdit.exe /s file
The /s means the file will be silent merged to the Registry. If the /s parameter is omitted the user will be asked to confirm the operation. In Windows 98, Windows 95 and at least some configurations of Windows XP the /s switch also causes RegEdit.exe to ignore the setting in the registry that allows administrators to disable it. When using the /s switch RegEdit.exe does not return an appropriate return code if the operation fails, unlike Reg.exe which does.
RegEdit.exe /e file
exports the whole registry to a .REG file, while any of
RegEdit.exe /e file HKEY_CLASSES_ROOT[\]
RegEdit.exe /e file HKEY_CURRENT_CONFIG[\]
RegEdit.exe /e file HKEY_CURRENT_USER[\]
RegEdit.exe /e file HKEY_LOCAL_MACHINE[\]
RegEdit.exe /e file HKEY_USERS[\]
export the specified (sub)key only.
The default association for .REG files in many versions of Microsoft Windows
Microsoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
.
We can use also Reg.exe. Here is a sample to display the value of the registry value Version:
Reg.exe QUERY HKLM\Software\Microsoft\ResKit /v Version
VBScript is an Active Scripting language developed by Microsoft that is modeled on Visual Basic. It is designed as a “lightweight” language with a fast interpreter for use in a wide variety of Microsoft environments...
JScript is a scripting language based on the ECMAScript standard that is used in Microsoft's Internet Explorer.JScript is implemented as a Windows Script engine. This means that it can be "plugged in" to any application that supports Windows Script, such as Internet Explorer, Active Server Pages,...
The Microsoft Windows Script Host is an automation technology for Microsoft Windows operating systems that provides scripting capabilities comparable to batch files, but with a greater range of supported features...
Windows Management Instrumentation is a set of extensions to the Windows Driver Model that provides an operating system interface through which instrumented components provide information and notification...
Windows PowerShell is Microsoft's task automation framework, consisting of a command-line shell and associated scripting language built on top of, and integrated with the .NET Framework...
.
Registry permissions can be manipulated through the command line using RegIni.exe and the SubInACL.exe tool. For example, the permissions on the HKEY_LOCAL_MACHINE\SOFTWARE key can be displayed using:
A programming language is an artificial language designed to communicate instructions to a machine, particularly a computer. Programming languages can be used to create programs that control the behavior of a machine and/or to express algorithms precisely....
s offer built-in runtime library functions or classes
Class (computer science)
In object-oriented programming, a class is a construct that is used as a blueprint to create instances of itself – referred to as class instances, class objects, instance objects or simply objects. A class defines constituent members which enable these class instances to have state and behavior...
that wrap the underlying Windows APIs and thereby enable programs to store settings in the registry (e.g. Microsoft.Win32.Registry in VB.NET
Visual Basic .NET
Visual Basic .NET , is an object-oriented computer programming language that can be viewed as an evolution of the classic Visual Basic , which is implemented on the .NET Framework...
Embarcadero Delphi is an integrated development environment for console, desktop graphical, web, and mobile applications.Delphi's compilers use its own Object Pascal dialect of Pascal and generate native code for 32- and 64-bit Windows operating systems, as well as 32-bit Mac OS X and iOS...
Free Pascal Compiler is a free Pascal and Object Pascal compiler.In addition to its own Object Pascal dialect, Free Pascal supports, to varying degrees, the dialects of several other compilers, including those of Turbo Pascal, Delphi, and some historical Macintosh compilers...
Component Object Model is a binary-interface standard for software componentry introduced by Microsoft in 1993. It is used to enable interprocess communication and dynamic object creation in a large range of programming languages...
Visual Basic is the third-generation event-driven programming language and integrated development environment from Microsoft for its COM programming model...
can use the WSH WScript.Shell object. Another way is to use the Windows Resource Kit Tool, Reg.exe by executing it from code, although this is considered poor programming practice
Programming style
Programming style is a set of rules or guidelines used when writing the source code for a computer program. It is often claimed that following a particular programming style will help programmers to read and understand source code conforming to the style, and help to avoid introducing errors.A...
A scripting language, script language, or extension language is a programming language that allows control of one or more applications. "Scripts" are distinct from the core code of the application, as they are usually written in a different language and are often created or at least modified by the...
Perl is a high-level, general-purpose, interpreted, dynamic programming language. Perl was originally developed by Larry Wall in 1987 as a general-purpose Unix scripting language to make report processing easier. Since then, it has undergone many changes and revisions and become widely popular...
Windows PowerShell is Microsoft's task automation framework, consisting of a command-line shell and associated scripting language built on top of, and integrated with the .NET Framework...
and Windows Scripting Host also enable registry editing from scripts.
Locations
The Registry is physically stored in several files, which are generally obfuscated from the user-mode APIs used to manipulate the data inside the Registry. Depending upon the version of Windows, there will be different files and different locations for these files, but they are all on the local machine. The location for system Registry files in Windows NT is \Windows\System32\Config; the user-specific HKEY_CURRENT_USER user registry hive is stored in Ntuser.dat inside the user profile. There is one of these per user; if a user has a roaming profile
Roaming user profile
A roaming user profile is a concept in the Microsoft Windows NT family of operating systems that allows a user with a computer joined to a Windows Server domain to log on to any computer on the same network and access their documents and have a consistent desktop experience, such as applications...
, then this file will be copied to and from a server
Server (computing)
In the context of client-server architecture, a server is a computer program running to serve the requests of other programs, the "clients". Thus, the "server" performs some computational task on behalf of "clients"...
at logout and login respectively. A second user-specific Registry file named UsrClass.dat contains COM registry entries and does not roam by default.
Windows NT-based operating systems
Windows NT-based systems store the registry in a binary hive format which can be exported, loaded and unloaded by the Registry Editor in these operating systems. The following system Registry files are stored in %SystemRoot%\System32\Config\:
Sam – HKEY_LOCAL_MACHINE\SAM
Security – HKEY_LOCAL_MACHINE\SECURITY
Software – HKEY_LOCAL_MACHINE\SOFTWARE
System – HKEY_LOCAL_MACHINE\SYSTEM
Default – HKEY_USERS\.DEFAULT
Userdiff – Not associated with a hive. Used only when upgrading operating systems.
The following file is stored in each user's profile folder:
In the context of the Microsoft Windows NT line of operating systems, a Security Identifier is a unique name which is assigned by a Windows Domain controller during the log on process that is used to identify a subject, such as a user or a group of users in a network of NT/2000...
> (linked to by HKEY_CURRENT_USER)
For Windows 2000, Server 2003 and Windows XP, the following additional user-specific file is used for COM information:
%UserProfile%\Local Settings\Application Data\Microsoft\Windows\Usrclass.dat (path is localized) – HKEY_USERS\_Classes (HKEY_CURRENT_USER\Software\Classes)
For Windows Vista and later, the path was changed to:
%UserProfile%\AppData\Local\Microsoft\Windows\Usrclass.dat (path is not localized) alias %LocalAppData%\Microsoft\Windows\Usrclass.dat – HKEY_USERS\_Classes (HKEY_CURRENT_USER\Software\Classes)
Windows 2000 kept an alternate copy of the registry hives (.ALT) and attempts to switch to it when corruption is detected. Windows XP and Windows Server 2003 do not maintain a System.alt hive because NTLDR
NTLDR
NTLDR is the boot loader for all releases of Windows NT operating system up to and including Windows XP and Windows Server 2003. NTLDR is typically run from the primary hard disk drive, but it can also run from portable storage devices such as a CD-ROM, USB flash drive, or floppy disk...
on those versions of Windows can process the System.log file to bring up to date a System hive that has become inconsistent during a shutdown or crash. In addition, the %Windir%\Repair folder contains a copy of the system's registry hives that were created after installation and the first successful startup of Windows.
Windows 95, 98, and Me
The registry files are stored in the %WINDIR% directory under the names USER.DAT and SYSTEM.DAT with the addition of CLASSES.DAT in Windows Me. Also, each user profile (if profiles are enabled) has its own USER.DAT file which is located in the user's profile directory in C:\Windows\Profiles\\.
Windows 3.11
The only registry file is called Reg.dat and it is stored in the C:\WINDOWS\ directory.
Backups and recovery
Different editions of Windows have supported a number of different methods to back up and restore the registry of the years, some of which are now deprecated:
System Restore is a component of Microsoft's Windows Me, Windows XP, Windows Vista and Windows 7, but not Windows 2000, operating systems that allows for the rolling back of system files, registry keys, installed programs, etc., to a previous state in the event of system malfunction or failure.The...
can back up the registry and restore it as long as Windows is bootable, or from the Windows Recovery Environment starting with Windows Vista.
NTBackup is the built-in backup application introduced in Windows NT around 1997 and part of all subsequent versions up to and including Windows 2000, Windows XP and Windows Server 2003. It uses a proprietary backup format to back up files. Files can be backed up to tape, ZIP drives, floppy...
Automated System Recovery is a feature of the Windows XP operating system that can be used to simplify recovery of a computer's system or boot volumes. ASR consists of two parts: an automated backup, and an automated restore...
in Windows XP can also restore the registry.
On Windows NT-based systems, the Last Known Good Configuration option in startup menu relinks the HKLM\SYSTEM\CurrentControlSet key, which stores hardware and device driver information.
Windows 98 and Windows Me include command line (Scanreg.exe) and GUI (Scanregw.exe) registry checker tools to check and fix the integrity of the registry, create up to five automatic regular backups by default and restore them manually or whenever corruption is detected. The registry checker tool backs up the registry, by default, to %Windir%\Sysbckup Scanreg.exe can also run from MS-DOS
MS-DOS
MS-DOS is an operating system for x86-based personal computers. It was the most commonly used member of the DOS family of operating systems, and was the main operating system for IBM PC compatible personal computers during the 1980s to the mid 1990s, until it was gradually superseded by operating...
Windows 95 is a consumer-oriented graphical user interface-based operating system. It was released on August 24, 1995 by Microsoft, and was a significant progression from the company's previous Windows products...
CD-ROM included an Emergency Recovery Utility (ERU.exe) and a Configuration Backup Tool (Cfgback.exe) to back up and restore the registry. Additionally Windows 95 backs up the registry to the files system.da0 and user.da0 on every successful boot.
Windows NT 4.0 is a preemptive, graphical and business-oriented operating system designed to work with either uniprocessor or symmetric multi-processor computers. It was the next release of Microsoft's Windows NT line of operating systems and was released to manufacturing on 31 July 1996...
included RDISK.EXE, a utility to back up and restore the entire registry.
Windows 2000 is a line of operating systems produced by Microsoft for use on personal computers, business desktops, laptops, and servers. Windows 2000 was released to manufacturing on 15 December 1999 and launched to retail on 17 February 2000. It is the successor to Windows NT 4.0, and is the...
Resource Kit contained an unsupported pair of utilities called Regback.exe and RegRest.exe for backup and recovery of the Registry.
Windows 2000 is a line of operating systems produced by Microsoft for use on personal computers, business desktops, laptops, and servers. Windows 2000 was released to manufacturing on 15 December 1999 and launched to retail on 17 February 2000. It is the successor to Windows NT 4.0, and is the...
Group Policy is a feature of the Microsoft Windows NT family of operating systems. Group Policy is a set of rules that control the working environment of user accounts and computer accounts. Group Policy provides the centralized management and configuration of operating systems, applications, and...
to enforce Registry settings. Policy may be applied locally to a single computer using gpedit.msc, or to multiple users and/or computers in a domain
Windows Server domain
A Windows domain is a collection of security principals that share a central directory database. This central database contains the user accounts and security information for...
Windows 95 is a consumer-oriented graphical user interface-based operating system. It was released on August 24, 1995 by Microsoft, and was a significant progression from the company's previous Windows products...
Windows 98 is a graphical operating system by Microsoft. It is the second major release in the Windows 9x line of operating systems. It was released to manufacturing on 15 May 1998 and to retail on 25 June 1998. Windows 98 is the successor to Windows 95. Like its predecessor, it is a hybrid...
Windows Millennium Edition, or Windows Me , is a graphical operating system released on September 14, 2000 by Microsoft, and was the last operating system released in the Windows 9x series. Support for Windows Me ended on July 11, 2006....
Windows NT is a family of operating systems produced by Microsoft, the first version of which was released in July 1993. It was a powerful high-level-language-based, processor-independent, multiprocessing, multiuser operating system with features comparable to Unix. It was intended to complement...
, administrators can use a special file to be merged into the registry, called a policy file (POLICY.POL). The policy file allows administrators to prevent non-administrator users from changing registry settings like, for instance, the security level of Internet Explorer
Internet Explorer
Windows Internet Explorer is a series of graphical web browsers developed by Microsoft and included as part of the Microsoft Windows line of operating systems, starting in 1995. It was first released as part of the add-on package Plus! for Windows 95 that year...
and the desktop background wallpaper. The policy file is primarily used in a business with a large number of computers where the business needs to be protected from rogue or careless users.
The default extension for the policy file is .POL.
The policy file filters the settings it enforces by user and by group (a "group" is a defined set of users). To do that the policy file merges into the registry, preventing users from circumventing it by simply changing back the settings.
The policy file is usually distributed through a LAN, but can be placed on the local computer.
The policy file is created by a free tool by Microsoft that goes by the filename poledit.exe for Windows 95/Windows 98 and with a computer management module for NT-based systems.
The editor requires administrative permissions to be run on systems that uses permissions.
The editor can also directly change the current registry settings of the local computer and if the remote registry service is installed and started on another computer it can also change the registry on that computer.
The policy editor loads the settings it can change from .ADM files, of which one is included, that contains the settings the Windows shell provides. The .ADM file is plain text and supports easy localisation by allowing all the strings to be stored in one place.
.INI file virtualization
Windows NT kernels support redirection of INI file-related APIs
Application programming interface
An application programming interface is a source code based specification intended to be used as an interface by software components to communicate with each other...
into a virtual file in a Registry location such as HKEY_CURRENT_USER using a feature called "InifileMapping". This functionality was introduced to allow legacy applications written for 16-bit
16-bit
-16-bit architecture:The HP BPC, introduced in 1975, was the world's first 16-bit microprocessor. Prominent 16-bit processors include the PDP-11, Intel 8086, Intel 80286 and the WDC 65C816. The Intel 8088 was program-compatible with the Intel 8086, and was 16-bit in that its registers were 16...
versions of Windows to be able to run under Windows NT platforms on which the System folder is no longer considered an appropriate location for user-specific data or configuration. Non-compliant 32-bit applications can also be redirected in this manner, even though the feature was originally intended for 16-bit applications.
Windows Vista is an operating system released in several variations developed by Microsoft for use on personal computers, including home and business desktops, laptops, tablet PCs, and media center PCs...
has introduced limited Registry virtualization, whereby poorly written applications that do not respect the principle of least privilege
Principle of least privilege
In information security, computer science, and other fields, the principle of least privilege, also known as the principle of minimal privilege or just least privilege, requires that in a particular abstraction layer of a computing environment, every module must be able to access only the...
and instead try to write user data to a read-only system location (such as the HKEY_LOCAL_MACHINE hive), can be redirected to a more appropriate location, without changing the application itself. The operation is transparent to the application, as it does not know that its Registry operations have been directed elsewhere.
Application virtualization is an umbrella term that describes software technologies that improve portability, manageability and compatibility of applications by encapsulating them from the underlying operating system on which they are executed. A fully virtualized application is not installed in...
redirects all of an application's Registry operations to a non-Registry backed location, such as a file. Used together with file virtualization, this approach allows applications to run without being installed on the location machine.
In the context of the Microsoft Windows range of operating systems, Mandatory Integrity Control or Integrity Levels is a core security feature, introduced in Windows Vista and Windows Server 2008, that adds Integrity Levels to processes running in a...
processes may also use registry virtualization. For example as Internet Explorer 7 or 8 running in "Protected Mode" on Windows Vista and above will automatically redirect registry writes by ActiveX controls to a sandboxed location in order to frustrate some classes of security exploits
Exploit (computer security)
An exploit is a piece of software, a chunk of data, or sequence of commands that takes advantage of a bug, glitch or vulnerability in order to cause unintended or unanticipated behavior to occur on computer software, hardware, or something electronic...
.
Lastly, the Application Compatibility Toolkit provides shims that can transparently redirect HKEY_LOCAL_MACHINE or HKEY_CLASSES_ROOT Registry operations to HKEY_CURRENT_USER to address "LUA
Principle of least privilege
In information security, computer science, and other fields, the principle of least privilege, also known as the principle of minimal privilege or just least privilege, requires that in a particular abstraction layer of a computing environment, every module must be able to access only the...
" bugs that cause applications not to work for limited users.
Equivalents in other operating systems
In contrast to the Windows registry's binary-based database model, some other operating system
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
In computing, plain text is the contents of an ordinary sequential file readable as textual material without much processing, usually opposed to formatted text....
In Unix and other multitasking computer operating systems, a daemon is a computer program that runs as a background process, rather than being under the direct control of an interactive user...
and application configuration, but group these configurations together for ease of management.
A Unix-like operating system is one that behaves in a manner similar to a Unix system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification....
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
The Filesystem Hierarchy Standard defines the main directories and their contents in Linux operating systems. For the most part, it is a formalization and extension of the traditional BSD filesystem hierarchy....
, system-wide configuration files (information similar to what would appear in HKEY_LOCAL_MACHINE on Windows) are traditionally stored in files in /etc/ and its subdirectories, or sometimes in /usr/local/etc. Per-user information (information that would be roughly equivalent to that in HKEY_CURRENT_USER) is stored in hidden directories and files (that start with a period/full stop) within the user's home directory
Home directory
A Home directory is a file system directory on a multi-user operating system containing files for a given user of the system. The specifics of the home directory is defined by the operating system involved; for example, Windows systems between 2000 and 2003 keep home directories in a folder...
. However XDG-compliant applications should refer to the environment variables defined in the Base Directory specification.
Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...
operating system typically store settings in property list
Property list
In the Mac OS X, iOS, NeXTSTEP, and GNUstep programming frameworks, property list files are files that store serialized objects. Property list files use the filename extension .plist, and thus are often referred to as p-list files....
files which are usually stored in each user's Library folder.
RISC OS is a computer operating system originally developed by Acorn Computers Ltd in Cambridge, England for their range of desktop computers, based on their own ARM architecture. First released in 1987, under the name Arthur, the subsequent iteration was renamed as in 1988...
also allows applications to be copied into directories easily, as opposed to the separate installation program that typifies Windows applications. If one wishes to remove the application, it is possible to simply delete the folder belonging to the application. This will often not remove configuration settings which are stored independently from the application, usually within the computer's !Boot structure, in !Boot.Choices, but potentially anywhere on a network fileserver.
IBM AIX (a Unix variant) uses a registry component called Object Data Manager
Object Data Manager
Object Data Manager is a database management system and device configuration integrated into IBM's AIX operating system. The ODM is unique to AIX compared to other UNIX operating systems. Data being managed by ODM is stored and maintained as objects with associated attributes...
(ODM). The ODM is used to store information about system and device configuration. An extensive set of tools and utilities provides users with means of extending, checking, correcting the ODM database. The ODM stores its information in several files, default location is /etc/objrepos.
GNOME is a desktop environment and graphical user interface that runs on top of a computer operating system. It is composed entirely of free and open source software...
desktop environment uses a registry-like interface called GConf
GConf
GConf is a system used by the GNOME desktop environment for storing configuration settings for the desktop and applications.Changes to this system are controlled by GConfd, a daemon. GConfd watches out for changes to the database, and when they are changed, it applies the new settings to...
for storing configuration settings for the desktop and applications. However, in GConf, all application settings are stored in separate files, thereby partially eliminating a single point of failure
Single point of failure
A single point of failure is a part of a system that, if it fails, will stop the entire system from working. They are undesirable in any system with a goal of high availability or reliability, be it a business practice, software application, or other industrial system.-Overview:Systems can be made...
The Elektra Initiative provides an alternative back-end for text configuration files for the Linux operating system.Instead of each program having its own text configuration files, with a variety of formats, Elektra tries to provide a universal, hierarchical, fast and consistent namespace and...
provides an alternative back-end for text configuration files for the Linux
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
Wine is a free software application that aims to allow computer programs written for Microsoft Windows to run on Unix-like operating systems. Wine also provides a software library, known as Winelib, against which developers can compile Windows applications to help port them to Unix-like...
A compatibility layer is a term that refers to components that allow for non-native support of components.In software engineering, a compatibility layer allows binaries for a legacy or foreign system to run on a host system. This translates system calls for the foreign system into native system...
, which allows Windows software to run on a Unix-like system, also employs a Windows-like registry as text files in the WINEPREFIX folder: system.reg (HKEY_LOCAL_MACHINE), user.reg (HKEY_CURRENT_USER) and userdef.reg.
A registry cleaner is a type of software utility designed for the Microsoft Windows operating system, the purpose of which is to remove redundant or unwanted items from the Windows registry....
Application virtualization is an umbrella term that describes software technologies that improve portability, manageability and compatibility of applications by encapsulating them from the underlying operating system on which they are executed. A fully virtualized application is not installed in...
logparser is a flexible command line utility that was initially written by Gabriele Giuseppini , a Microsoft employee, to automate tests for IIS logging. It was intended for use with the Windows operating system, and was included with the IIS 6.0 Resource Kit Tools...
The Windows registry can be edited manually using programs such as regedit.exe and on older versions of Windows, regedt32.exe, although these tools do not expose some of registry's metadata such as the last modified date. They also implement workarounds in code that allow Registry keys to be renamed, as the underlying APIs do not support this capability.