Summary

Synopsis

During run time, MSI setups use Microsoft's MSI engine to install files, create shortcuts, registry keys, etc. Because the MSI engine is the driving force of such a setup, it follows MSI guidelines to update files.

Discussion

There are two different sets of rules that are taken into consideration when updating file: the overwriting of versioned files and the overwriting of non-versioned files. By default, the MSI engine makes sure that a file with the latest version prevails on the system. Thus, to overwrite a versioned file, you must update the version number of that file in your subsequent upgrade. The following are some file versioning rules that the MSI engine follows while updating or overwriting files.

1. Versioned File
   1. If the file version on the target system is the same as that in the setup package, the file is not updated, irrespective of the date.

   2. If the file version on the target system is older than that in the setup, the file is overwritten.

   3. If the file version on the target system is newer than the file within the setup, it is not overwritten.

2. Non-Versioned File
   1. If the file on the target system has a later modified date versus created date, it is not overwritten, as it is considered user data.

   2. If the file on the target system has the same created and modified date, it is overwritten.

   3. If the file on the target system has a created date that is later than the modified date, it is overwritten.

Additional Information

The default overwriting rules can be overridden by setting the REINSTALLMODE property. For more information on overriding the default rules using the REINSTALLMODE property, see the Windows Installer Help LIbrary topic REINSTALLMODE Property.

For more information on File Versioning Rules, see the Windows Installer Help topic File Versioning Rules.