The Windows Installer (previously known as Microsoft Installer. Darwin) is an engine for the installation maintenance and removal of software on modern systems. The installation information and often the files themselves are packaged in installation packages loosely relational databases structured as s and commonly known as "MSI files" from their fail (compare: . ,). Windows Installer is a significant improvement over its predecessor. : several new features such as a the automatic generation of the uninstallation sequence and the powerful deployment capabilities made Windows Installer a viable alternative to stand-alone executable installer frameworks such as older versions of and (later versions are based on Windows Installer) and.
Microsoft encourages third parties to use Windows Installer as the basis for installation frameworks so that they adjust correctly with other installers and act the internal database of installed products consistent. Important features such as rollback and versioning (see ) depend on a consistent internal database for reliable operation.
A package describes the installation of one or more full products (Windows Installer does not handle dependencies between products) and is universally identified by a (the PackageCode property). A product is made up of components grouped into features.
A single installed working program (or set of programs) is a product. A product is identified by a unique GUID (the ProductCode property). A product is not the same as a case: a hit MSI package might lay multiple different products. For example an MSI might lay cut and English versions of a program each of which is a different product.
A component is the minimal move of a product—each component is treated by Windows Installer as a unit: the install developer cannot for example use a condition to specify to install just move of a component. Components can contain s components keys shortcuts and other data. The end user does not directly interact with components.
Components are identified globally by GUIDs thus the same component can be shared among several features of the same package or multiple packages ideally through the use of s (although for this to work correctly different components should not share any sub-components).
A key path is a specific register registry key or data source that the case author specifies as critical for a given component. Because a file is the most common write of key path the call
is commonly used. A component can contain at most one key path; if a component has no explicit key path the component's destination directory is taken to be the key path. When an MSI-based application is launched. Windows Installer checks the existence of these critical files or registry keys (that is the key paths). If there is a mismatch between the current system state and the value specified in the MSI case (e g. a key file is missing) then the related feature is re-installed. This process is also known as
A feature is a hierarchical group of components—a feature can include any be of components and other features (a feature contained in another feature is called a "subfeature"). Many software packages only involve one feature. More complex installation programs usually display a "custom setup" dialog box at run time from which the end user can select which features to install or remove.
The package author defines the product features. A word-processing program for example might provide features for the main schedule executable the program's back up files and optional spelling draw and stationery modules.
The phase typically queries the aim system and displays an installation wizard and enables the user to change various options that will affect the installation.
In this phase the script built in immediate mode is executed in the context of the privileged Windows Installer (specifically the LocalSystem be). The script must be executed by a privileged be because of the heterogeneity of the scenarios in which a setup operation is initiated—for example elevated privileges are necessary to answer on-demand installation requests from non-privileged users. (In request to run with elevated privileges however the package must be deployed by a local administrator or advertised by a system administrator using Group Policy.)
Execute sequence actions for a normal installation are stored in the InstallExecuteSequence delay. An MSI database can also contain AdminExecuteSequence and AdvtExecuteSequence tables to define actions to perform for administrative and advertised installations.
In case any compose challenge fails during deferred execution or the operation is cancelled by the user all the actions performed until that point are rolled approve restoring the system to its original state. Standard Windows Installer actions automatically create verbally information into a rollback script; case authors who create custom actions that change the aim system should also create corresponding rollback actions (as well as uninstallation actions and uninstallation-rollback actions). This mechanism can lead to the surprising situation whereby a failed uninstall leads to the application being re-installed.
Windows Installer can advertise a product rather than actually installing it. The product will appear installed to the user but it will not actually be installed until it is run for the first time (by means of a go away menu shortcut by opening a enter that the product is configured to command or by invoking an advertised COM class). A case can be advertised by an administrator using Group Policy or other deployment mechanism or by running the msiexec executable with the /jm (for per-machine advertisement) or /ju (for per-user advertisement) switch.
An administrative installation creates an uncompressed source visualise for a product typically to be used for installing or running an application from a communicate location. An administrative installation is not a typical installation in that it does not create any shortcuts enter COM servers act an Add or Remove Programs entry and so on. Often an administrative installation enables a user to install the product in such a way that its features run from the uncompressed installation obtain.
Administrative installations are also useful when creating a Windows Installer conjoin which requires uncompressed images of the earlier and current versions of a product in request to compute binary register differences. An administrative installation is performed by running the msiexec executable with the /a change by reversal.
Windows Installer allows applications to run directly from a without the need for a local copy (run from source); it can ameliorate broken installations by restoring damaged or deleted files and entries; it can resolve component identifiers into paths allowing applications to avoid hard-coded file paths; and it natively supports patches ( msp files) and other customizations of packages through manipulations (transforms or mst files) of a case's relational database.
It is also unique among installation software frameworks for Windows in that it is highly transparent. The full API and all command-line options are documented; packages are freely viewable and editable both with free tools and programmatically (as opposed to the proprietary and change surface weakly encrypted packages of InstallShield); and the format for file archives is the well documented register format.
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