Merge Modules: A Little Background, Please

Merge modules provide a standard method by which developers deliver shared Windows Installer components and setup logic to their applications. Merge modules are used to deliver shared code, files, resources, registry entries, and setup logic to applications as a single compound file. Read on to learn more.

About Merge Modules

A merge module is similar in structure to a simplified Windows Installer .msi file. However, a merge module cannot be installed alone, it must be merged into an installation package using a merge tool.When a merge module is merged into the .msi file of an application, all the information and resources required to install the components delivered by the merge module are incorporated into the application's .msi file.

Merge modules are essentially simplified .msi files, which is the file name extension for a Windows® Installer installation package. A standard merge module has an .msm file name extension.

A merge module cannot be installed alone because its lacks some vital database tables that are present in an installation database. Merge modules also contain additional tables that are unique to themselves. To install the information delivered by a merge module with an application, the module must first be merged into the application's .msi file.

A merge module consists of the following parts:

• A Merge Module Database containing the installation properties and setup logic being delivered by the merge module.
• A Merge Module Summary Information Stream Reference describing the module.
• A MergeModule.CABinet cabinet file stored as a stream inside the merge module. This cabinet contains all the files required by the components delivered by the merge module.