Create 2025-08-05-msi-and-mst-files.md

Author: robertmuehsig

_posts/2025-08-05-msi-and-mst-files.md

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+---
+layout: post
+title: "MSI and MST files"
+description: "A (very) short overview of how MSI and MST files work together..."
+date: 2025-08-05 23:59
+author: Robert Muehsig
+tags: [Windows, Installer]
+language: en
+---
+
+{% include JB/setup %}
+
+*This is more of a "Today-I-Learned" post and not a "full-blown How-To article." If something is completely wrong, please let me know – thanks!*
+
+# What is an MSI?
+
+Let's start simple: An __MSI__ (Microsoft Installer) is a package used to install software on Windows. The MSI contains everything needed to install the software, such as files, registry changes, and custom actions.
+
+An MSI also includes *properties*—for example, the install location or custom values that need to be applied during installation.
+
+You can install an MSI interactively (by double-clicking it) or by using the `msiexec` command.
+
+A more complex `msiexec` command can look like this:
+
+```
+msiexec /qb /i "installer.msi" APPLICATIONFOLDER="C:\Program Files\customSoftware" SOMEPROP="SomeValue" SOMEOTHERPROP="SomeOtherValue"
+```
+
+# Ok... and what is an MST?
+
+An __MST__ (Microsoft Transform) is a file that contains a set of modifications for an MSI installation. All those properties (and more) that you would pass via command line can be "baked into" an MST file.
+
+You can apply an MST during installation like this:
+
+
+```
+msiexec /i setup.msi TRANSFORMS=custom.mst /qn
+```
+
+
+# Pros / Cons
+
+**Pros:**
+
+If you want to apply the same settings across multiple installations and keep them stored in one place, an MST is a good solution.
+
+**Cons:**
+
+The MST file, like the MSI itself, is a binary file and can only be edited with tools like [Orca](https://learn.microsoft.com/en-us/windows/win32/msi/orca-exe).
+
+Both file formats are quite old, but I recently learned that **MST** files are still a thing—and quite useful if you're dealing with automated or enterprise software deployments.
+
+Hope this helps!