Without the MSI installer, also known as the Microsoft Windows Installer, you would not be able to install most of your favorite programs on your Windows computer. Microsoft previously referred to it as the Microsoft Installer, and some call it the MSI installer because it installs files with the .msi extension. The installer provides installation and configuration services for the Windows operating system.
The Windows Installer uses information provided by an application developer to install and configure a program. During the installation, the installer also displays a series of screens known as the setup user interface. The interface enables the user to select the features to install and to specify the location to install the program. The installer carries out all the installation and configuration tasks without requiring the user to know anything about the actions it performs.
To use the Windows Installer to install a program, an application developer must author an installation package for the program. The package, whose file extension is .msi, contains all the information required by the installer to install or remove a program and to run the setup user interface on a Windows computer. The package also contains a database, which stores the information required to perform the installation. Application developers use free or commercial package development tools to create installation packages.
The Windows Installer package author specifies features and components when he creates the package. The installer uses this information to perform its operations. For example, when you install a program, you can optionally select which features of the program to install. Also during the installation, the Windows Installer installs the program's components, which are the software files that make up the program, onto the computer. The installer gets the information about the features and components from the installation package. The installer also uses the information from the package when you remove a program using the Windows program removal feature on the Control Panel.
During an installation, the Windows Installer creates an installation script based on the instructions stored in the package database. As it creates the installation script, the installer also creates a rollback script. If the installation fails, the installer uses the rollback script to return the computer to its state before the installation began. This ensures that a failed installation does not cause any problems on the Windows computer.
In addition to installation and configuration, the Windows Installer also provides other benefits, including component management. During the installation of a program, the installer stores information about the program installation in an installation database. The installation database maintains information about the components required by programs, the files that make up components and the locations of component files and sources.