Server Administrator Version 8.5 Installation Guide — Microsoft Windows

The Microsoft Software Installer (MSI) provides the ability to return a system to its fully working condition after a failed installation. MSI does this by maintaining an undo operation for every standard action it performs during an install, upgrade, or uninstall. This operation includes restoration of deleted or overwritten files, registry keys, and other resources. Windows temporarily saves all files that it deletes or overwrites during the course of an installation or removal, so that they can be restored if necessary, which is a type of rollback. After a successful installation, Windows deletes all of the temporary backup files.

In addition to the rollback of MSI Standard Actions, the library also has the ability to undo commands listed in the INI file for each application if a rollback occurs. All files that are modified by the installation actions are restored to their original state if a rollback occurs.

When the MSI engine is going through the installation sequence, it ignores all actions that are scheduled as rollback actions. If a Custom Action, MSI Standard Action, or a installation action fails, then a rollback starts.

You cannot roll back an installation once it is completed; transacted installation is only intended as a safety net that protects the system during an installation session. If you want to remove an installed application, you should uninstall that application.