Benefits of Windows Installer Some of the features and benefits of windows installer are Elevated Privileges : A windows installer package deployed by an administrator runs with elevated privileges, in which the installer can perform operations that a locked down user could not perform. An installation running with elevated privileges can write to the program files folder, (c:\program files) where the applications are mostly installed until and unless changed by you., and to HKEY_LOCAL_MACHINE registry Key. Rollback Installation : Windows Installer keeps track of all the changes it makes to a computer. Therefore, if you attempt to add, modify, or remove an application and the action fails, Windows Installer restores the computer to its previous state. The restoration procedure is known as a rollback, When the Windows Installer processes the installation script for the installation of a product or application, it simultaneously generates a rollback script describing the system changes that have been made so far, and saves a copy of every file deleted during the installation. These files are kept in a hidden system directory and are automatically deleted once the installation is successfully completed. If however the installation is unsuccessful, the installer automatically performs a rollback installation that returns the system to its original state. Automatic rollback of an unsuccessful installation is the default behavior of the installer. Advertisement : The Windows Installer can advertise the availability of an application to users or other applications without actually installing the application. If an application is advertised, only the interfaces (Shortcuts) required for loading and launching the application are presented to the user or other applications. If a user or application activates an advertised interface the installer then proceeds to install the necessary components as described in Installation-On-Demand. The two types of advertising are assigning and publishing. An application appears installed to a user when that application is assigned to the user (This assignment is done from an SMS server or through Active directory or any other means of deployment). The Start menu contains the appropriate shortcuts, icons are displayed, files are associated with the application, and registry entries reflect the application's installation. When the user tries to open an assigned application it is installed upon demand. An application can only be published from a Windows 2000 Server. The published application is then installed by Windows 2000 through its file association or Multipurpose Internet Mail Extension (MIME) type. Publishing does not populate the user interface with any of the application's icons. Operating systems other than Windows 2000 cannot install a published application. Self Repair : When a product installed with windows installer is launched from its shortcut, MSI can detect and reinstall missing resources. In addition the add remove program in the control panel supports a repair option for each product which detects and the installs missing data. In a legacy setup if some of the files are missing then the application crashes or makes the operating system unstable. With msi the application can self repair itself without the need for an administrator to come visit the system and reinstall the application. For a self repair to work the source from which the application has been installed should be available. Usually in corporate environments the source will be located on a network drive. Transforms : Many of the applications these days are msi’s. the software developer or the vendor is packaging the applications now in MSI. A vendor msi should never be repackaged under any circumstances. We can customize the vendor msi using transforms. On-demand installation : Using Windows Installer, you can configure applications to initially install a minimal subset of features. Later, when a user selects a feature for the first time, additional components, required by that feature are automatically installed. For example, you can configure Windows Installer to install a word processor application that has a minimal set of features. The first time a user attempts to access a mail merge function included with the original installation, Windows Installer installs the mail merge component. You can modify the feature set that you want to install initially to balance disk usage, and the number of on-demand installs that a user can take advantage of. Windows installer supports a standard procedure for customizing an MSI database, through the use of windows installed transforms.