What are Merge Modules

Merge modules are a mechanism in Windows Installer that allows software companies to
prepackage and share standard component definitions. For example, take the infamous Crystal
Reports runtimes. The files, DLLs, and registry entries that make up these runtimes can be
defined as Windows Installer components and placed in a merge module.
When any developer in the world wants to distribute these runtimes, they use the vendor merge
module to ensure that a complete set of runtimes files is included with the vendor assigned
versions, component codes, registry keys, and other Windows Installer elements that the owning
software vendor assigned. Obviously one of the biggest publisher’s of merge modules is
Microsoft. When not merged into a package, merge modules are contained in .MSM files
(another variant on the .MSI format).