November 18, 1999

During installation of Microsoft Office 2000, Windows® Installer creates a file that contains the names and locations of all files and registry settings that are removed by the new installation. The list of items to remove is based on default settings in Windows Installer or settings specified on the Remove Previous Versions panel of the Custom Installation Wizard.

Every file and registry entry removed by Windows Installer is also saved in a hidden folder. When the installation is successfully completed, the hidden folder and all its files are deleted. This functionality is called the rollback feature of Windows Installer. Because these files take up considerable disk space on the hard drive, you can disable the rollback feature when you install Office on users’ computers.

Caution   Disabling the rollback feature of Windows Installer is not a recommended procedure for most installation scenarios. However, it can be useful when local hard disk space is very limited.

When the rollback feature is activated, and an Office 2000 installation fails or a user cancels Setup before the process is complete, Windows Installer refers to the locations file and hidden folder to undo the installation. This process removes all the files and registry settings created by Windows Installer up to the point of the interruption, and then reinstalls any files or registry entries that were removed.

The rollback feature allows you to recover gracefully from a computer or power failure. However, the rollback feature can consume a large amount of disk space during installation – particularly when you are removing multiple applications.

If you need to conserve disk space when you install Office 2000, you can turn off the Windows Installer rollback feature by setting the DISABLEROLLBACK property to 1 on the Setup command line. For example:

<path>\setup.exe DISABLEROLLBACK=1

Tip    You can also use a system policy to disable the rollback feature for all the users in your organization. In the System Policy Editor, set the Default User\Windows Installer\Disable rollback policy. Note that the Disable Rollback policy must be set on a per-user basis only, and not a per-computer basis.

When you turn off the rollback feature, it is more difficult to recover from an installation failure. For example, if the DISABLEROLLBACK property is set to 1, and you cancel Setup during the installation process, some features might be only partially removed or installed. You might also end up with conflicting settings in the Windows registry.

If the installation fails without manual cancellation (for example, because of a power loss or computer failure), Windows Installer stops in an installation-in-progress state. When you rerun Setup and restart Windows Installer, you receive one of several error messages.

These error messages state that an installation is in progress and might instruct you to undo your previous installation or restore the computer to its previous state before continuing with the new installation. However, because the rollback feature has been disabled, you cannot undo the interrupted installation or restore your original configuration.