The Windows Installer Service

The installation, management, and removal of applications that display the Designed for Windows logo, and many applications that do not display the logo, are performed by the Windows Installer service. The Windows Installer service runs quietly in the background just like any other Windows service and can be enabled and displayed using the Computer Management Console.

Note 

Detailed information on the Computer Management Console and how to use it to administer Windows services can be found in "Services and Applications" in Chapter 10, Microsoft Management Consoles.

The Add or Remove Programs utility provides an interface for working with the Windows Installer service. Using the Add or Remove Programs utility and the Windows Installer service, administrators can manage an application's entire life cycle, from initial installation to upgrade and finally to removal.

Note 

Administrators have to manually manage and administer applications that do not register themselves with the Windows Installer service. Many such programs provide their own uninstall programs and depend on vendor specific instruction for maintenance and repair. Occasionally administrators may come across applications that do not provide uninstall programs. To remove these programs from a computer, administrators must rely on vendor documentation to remove the application or may have to use Windows Explorer to try and locate and remove as many of the application's components as possible.

Since it is a service, administrators do not work directly with Windows Installer. Instead, the primary way of working with it is through the Add or Remove Programs dialog. Applications that register with Windows Installer contain an .MSI file that provides the services with detailed application information. This information includes identifying critical application components. Windows Installer verifies the presence and integrity of these critical components every time the application is started. In the event that something happens to a critical file that may hamper or even disable the operation of the application, the Windows Installer will automatically attempt to repair the application by replacing the missing or corrupted file. As a result, a prompt may appear asking for the application's source media so that the service can replace the damaged or missing file. Once fixed, the application is loaded and allowed to run without interference.

The Windows Installer service makes application installation and removal run smoother. During application install, the service tracks the files and registry keys created or modified by the application's setup program. If a problem occurs during installation, the service can then use this information to undo any changes or additions to the system and restore the computer to its previous state. Tracking all the changes made to the computer during installation helps ensure a clean uninstall when the time comes.

Another way that the Windows Installer service improves application and system stability is by preventing applications from changing or deleting files that are critical to the operation of other applications or the operating system. To accomplish this, the Windows Installer service keeps track of which applications require which files. Then, for example, if an application's uninstall process attempts to delete a file that the service knows is a critical file for another application, the service prevents it from being deleted.