Windows installation formats: MSI and MSIX

Posted: (EET/GMT+2)

 

If you need to install applications on Windows, you will usually run into two formats: .msi and .msix. Here is a quick comparison of what they are and when to use each.

MSI (Windows Installer, aka "Microsoft Installer") has been around for a long time, at least since 1999, and is still widely used for traditional desktop applications. MSIX is the newer packaging format from Microsoft, designed for modern, more predictable installations. It was announced in 2016.

Here is a practical comparison between the two.

The MSI format:

  • Traditional Windows Installer format
  • Used by many existing desktop applications
  • Supports complex installation logic and custom actions
  • Can modify system state (registry, files, services) freely
  • Requires manual cleanup logic on uninstall in some cases.

The MSIX format:

  • Modern packaging format (based on AppX)
  • Designed for clean install and uninstall
  • Runs applications in a more isolated environment
  • Automatic cleanup on uninstall
  • Built-in support for signing and integrity validation.

One key difference is how installations are handled. MSI packages can run custom scripts and make changes across the system. This is flexible, but it can also lead to inconsistent states if something fails.

MSIX takes a more controlled approach. The application is installed in a managed way, and the system tracks what was added. When you uninstall, everything is removed cleanly.

Another difference is isolation. MSIX applications run with more restrictions compared to MSI-based applications. This improves reliability and security, but it also means some older installation patterns do not work without changes.

From a practical point of view:

  • Use MSI for existing applications that rely on full system access or complex installation steps.
  • Use MSIX for new applications when you want predictable installs, clean uninstall, and better isolation.

MSIX is the direction Microsoft is pushing for new development, but MSI is still fully supported and commonly used, especially in enterprise environments.