Microsoft Windows Installer Service
The Windows Installer Service in Windows is used to install applications and services. Most new applications come in pre-packaged files, known as Microsoft Installer Files (MSI Files).
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Windows Installer files contain application setup and installation information. Windows installer tracks the location of all groups of files, registry entries, and shortcuts that are installed and can cleanly perform uninstall/removal tasks. Because Windows Installer tracks the location of any components it installs, failed installations can also be repaired. Any Microsoft operating system before Windows 2000 used the installer service provided by the application. Legacy clients are unable to make full use of the Windows installer service. Older operating systems used standard .exe files. The installer service can be downloaded for older clients, which will allow them to use .msi files. Using the Windows Installer Service alongside Active Directory, applications can be centrally stored and installed automatically to clients on the domain. Only Windows 2000/XP/2003 machines can make use of this feature.
Microsoft Installer (MSI) Files
Windows Installer packages are packaged into .MSI files, which is a database file that describes the configuration settings of the application. Windows Installer runs .MSI packages natively, as it does .EXE files. Unlike EXE installations, Windows Installer installations can monitor the state of the installation and even roll it back should something go wrong. That flexibility is not afforded using traditional EXE files.
Using Active Directory and group policy, MSI files can be automatically installed on client machines when the machine boots up.
Using group policy, specified users and computers on a domain can have different applications installed. For example, if Microsoft Office has been assigned to a specific user who goes to a machine without Office installed on it, Office will automatically be installed on that machine.
Using group policy, MSI files can be either assigned to a user or computer. If the application is assigned to a computer, then the application will be installed on that computer when it reboots and will then be available to all users who are using that machine. If the application is assigned to a user, then whichever computer the user logs onto (Windows 2000/XP/2003), the application will appear to be installed. Installation will be invoked if the user attempts to open the application.
MSI files can also be published to a user on the domain. If an application is published to a user, it will appear in the Add/Remove Programs wizard. The MSI file doesn’t need to be stored on the client. Applications cannot be published to a computer.
Microsoft Transform (MST) Files
Extensive modifications to the installation process can be made using a Microsoft Transform (MST file), including many modifications that cannot be made through the Setup command line or settings file. Using MST files, applications can be installed in different ways for different users. e.g. Office may only install with Microsoft Word for one user and Microsoft Excel for another. MST files can be published or assigned alongside MSI files to automatically customize the installation for users on the network.
For example using an MST file for Office, the following can be customized:
- Where Microsoft Office is installed
- Which Office features are installed
- Where Office shortcuts are installed
- What previous versions of Office are removed
- How Setup property values are set
Custom files and registry entries can also be added to the installation. You create a MST by using the tools provided with the software (Office Resource Kit). The Windows installer applies your changes to the Windows installer package (MSI file) before installing it.
Using .zap files is an alternative to using .msi files. Basically, a .zap file is a text file than can be used for software installation. Any text editor can be used to create a .zap file. ZAP files allow developers to package application without making large .msi files. ZAP files are also used for older applications.
Unfortunately .zap files have limitations and offer less functionality than Windows Installer files. ZAP files should only be used when there is no alternative. Note the following limitations:
- .zap files can only be published. They cannot be assigned.
- .zap files will not attempt to repair themselves if files are deleted or corrupted.
- Most .zap files require user intervention during installation.