What is Windows Installer? It is software from Microsoft Corporation that is used for installing, administrating and removing applications on a computer that runs Windows Operating System.
You may be familiarized with such installation programs like InstallShield, WISE, Setup API. Windows Installer is the latest one in this genre. It has several features that make it a powerful and a very useful tool in package installation, maintenance and removal as well as maintaining the internal database of installed applications stable.
So what makes Windows Installer special? Among many of its common features advertising is one that is new and should be explained, I think.
Instead of actually installing a product on your windows box, now you can just advertise it. This is a part of what is known as Installation-On-Demand strategy. Only the interfaces responsible for loading and launching a product are initiated. If the user or any application needs the product, they can activate the advertised interface and then the installation of the advertised product happens.
Advertising is classified into two categories: assigning and publishing. In assigning, an application seems to be installed, with visible registry entries. You can see the shortcut menu to the application and also you can find it in the start menu. Only when the user opens the application, the application gets installed.
Microsoft incorporated the facility of publishing an application from a server starting from Windows 2000 Server onwards. The published application can get installed with the help of MIME (Multipurpose Internet Mail Extension) or associated files.
Installation of certain features in an application on demand is another notable feature supported by Windows Installer.
Other features include support for administrative installation of an application, which is helpful in creating Windows Installer patch. This feature helps in computing the binary difference between the early and current version of an application.
If an installation is unsuccessful, Windows Installer restores the original state of the computer with the help of its rollback feature. When the installer is in the process of installing an application, it runs a script that generates a rollback script. In addition to the rollback script, the installer saves a copy of every file it deletes during the installation. If the installation is completed successfully, the rollback script and the saved files are deleted. Or else, on unsuccessful installation the rollback script is executed and the system is restored to the original state.