Codenamed ‘Darwin’ the Microsoft Installer bought to the software packaging industry a much needed element of competition. Before the Microsoft Installer (now known as the windows installer) the packaging and distribution of software was dominated by stand alone installation packages from InstallShield and WISE. With the windows installer engine, Microsoft has ensured that the monopoly that InstallShield had when it came to packaging and distribution of software ended. Many other companies have tried unsuccessfully to follow Microsoft’s lead and provide their own packaging and distribution engine. Today windows installer is preferred by all major software manufacturers to distribute their software packages and windows installer is expected to be the most popular packaging engine in coming time.
Windows installer allows end users to customize their installations at run time, in fact windows installer is well known for its high scalability when it comes to developing distribution packages. The basic unit of any windows installer package (MSI package) is a component. A component is comparable to an atom, and it is the building block of any MSI package. Sometimes a corrupt MSI package can be missing important components in which case the installation of the product cannot proceed. Windows installer has an inbuilt mechanism that verifies the contents of each MSI package to ensure that all important components of the package are available before the installation begins.
Similar to an inventory check, the windows installer has a list of all important components and every time an installation is initiated the windows installer checks the ‘manifest’ to ensure that no component is missing. The end user does not have direct access to the components and the windows installer manages the file associations and registration of key files. The key files can be registry components, ODBC connections etc. In a nutshell the windows installer takes care of the installation and registration of files without much user intervention.
In addition to components and key files, an important feature of the windows installer is allowing a user to customize the installation of a MSI package. Features are a group of components and key files that can be removed without effecting the installation of the software. Essential features of software are not customizable and the user cannot choose to not install essential features of a software. For example, during the installation of larger software packages the end user has a choice which features he wishes to install, however during the installation some features are greyed out indicating that they are essential features and the end user has to install them to ensure functioning of the software.
Although windows installer is a GUI (Graphical User Interface) based installer, a user can bypass the GUI installation by installing the software in command prompt by executing the file msiexec.exe, such an installation of the software is a called ‘installing the software in quite mode’. Quite mode installations are recommended for expert users only. The most common method of installing windows installer based software is to simply double click on the setup or msiexec.exe file. The windows installer kicks in and the installation of the software can be completed by following the instructions on screen.

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