Comparing MSI vs. MSIX

What is MSI?

MSI, or Microsoft Installer, is a Windows-specific installation and configuration service that has been a cornerstone of software deployment for over two decades. Introduced in the late 1990s, MSI packages applications in a format that Windows Installer can execute, simplifying the installation process and ensuring consistency. Windows Installer is another commonly used name for MSI.

Benefits of using MSI

With the introduction of MSI, Microsoft streamlined the process of deploying and managing centralized applications. There are lots of benefits of the MSI format, including the following:

• Standardization. MSI provides a standardized method for application installation, making it easier for IT administrators to manage software across a wide range of devices.
• Customizability. IT administrators can customize MSI files through transforms -- .mst files -- allowing for tailored installations that meet specific enterprise requirements.
• Rollback and repair. One of the standout features of MSI is its ability to roll back installations if something goes wrong. Additionally, MSI supports self-repair, which could fix corrupted installations automatically.
• Administrative installation. MSI supports administrative installations, enabling network-based installations that save time and bandwidth.
• Integration with Group Policy. MSI integrates seamlessly with Group Policy in Active Directory environments, allowing IT to centrally manage application deployments.

IT departments have used MSI deploying standard desktop applications in Windows environments. Its feature has made it an ideal format for large-scale deployments where version consistency, scalability and manageability are paramount.

However, MSI-based applications can leave residual "rot" on the OS. When admins uninstall an MSI package, application files in AppData and registry entries from the app's usage often remain on the machine, cluttering the system. This phenomenon, commonly known as Windows rot, can slow down a PC with each new installation.

Microsoft aimed to address this issue with the MSIX format, ensuring that when an application or package is uninstalled, all references to the application are completely removed from the system.

What is MSIX?

Microsoft introduced MSIX in 2018 as an enhanced version of the AppX package format, which was initially used exclusively for Universal Windows Platform apps. The goal of this format was to better accommodate traditional desktop applications on Windows 10. Microsoft tried to apply insights from MSI, App-V packages and the Desktop Bridge program when it designed and released MSIX.

However, in the original announcement, Microsoft also indicated that the road to MSIX would be a journey and it would take several releases to complete all the functionality needed.

Looking at MSIX structurally, it is a package format that is similar to an AppX or App-V package. Essentially, it is a zip file that includes the application files and configuration XML files.

MSIX supports modern development practices while still providing extensive support for older Win32 applications, including traditional x86 and x64 unmanaged-code apps and .NET Framework-based applications. This means admins can package a standard desktop application using the new MSIX format and deploy it using existing tools such as Configuration Manager and Intune.

Benefits of using MSIX

MSIX also came with some new capabilities and benefits that differentiate it from MSI, including the following:

• Universal packaging format. Admins can use MSIX packages across different types of Windows devices, from desktops to mobile devices, offering a unified approach to application deployment.
• Enhanced security. MSIX provides a secure installation process by ensuring that packages are signed and validated. This reduces the risk of malicious software, unlike MSI.
• Efficient updates and bandwidth savings. With MSIX, updates are more efficient. The technology supports differential updates, meaning only the changed aspects of an application need to be downloaded. This reduces bandwidth and installation time to the client or server.
• State management. MSIX includes built-in support for application state management, ensuring that user settings and data are preserved across updates.
• Containerization. Applications installed using MSIX can run in a lightweight container, isolating them from the system and other applications similar to App-V.
• Backward compatibility. MSIX also supports existing Win32, WPF and WinForms applications, making it easier for developers to transition to this new format without extensive rewrites.

When Microsoft initially released MSIX, many organizations were reluctant to switch over because it had its share of bugs and did not have proper tooling to convert applications. Additionally, organizations using App-V also experienced limitations with the containerization feature. App-V packages could not convert directly to MSIX-based applications with the same level of features. Since then, many organizations started to move some applications from App-V, since Microsoft has defined its end of life as 2026.

Tools that can help organizations move to MSIX

Fortunately, there are more tools evolving within Microsoft and the surrounding community to help the adoption and ease of converting applications from MSI to MSIX.

When Microsoft initially released MSIX, many organizations were reluctant to switch over because it had its share of bugs and did not have proper tooling to convert applications.

This includes tools such as the MSIX Package Support Framework and MSIX Packaging tool from Microsoft. Also, other tools such as TMEditX which is a tool designed for editing MSIX packages to integrate the Package Support Framework and enhance application compatibility. It excels at analyzing the original intent of MSI/EXE installers to provide strong compatibility within the MSIX ecosystem. Additionally, TMEditX can also convert packages to AppAttach formats, further extending its utility.

There are also vendors such as Citrix and VMware that now support the MSIX format within their VDI platforms. This ensures simpler management to use MSIX applications.

Evaluating MSI vs. MSIX

The advantages of MSIX are clear, but its success hinges on widespread adoption by both enterprise organizations and independent software vendors (ISVs). For example, Microsoft is now packaging Office as an MSIX package, and the latest version of Microsoft Teams is also available as an MSIX package.

When Microsoft introduced MSI, it quickly became the preferred repackaging format in enterprise organizations, leading vendors to adopt it widely. This is why it remains for many the default format today. Similarly, App-V saw considerable usage within enterprise organizations but could never completely replace MSI and did not gain much traction with vendors. Organizations often use it for its containerization features to ensure application compatibility.

This struggle is now happening with MSIX, which is why MSIX hasn't seen the full-scale adoption of the format from the larger ISVs. There are not many incentives for them to switch to another format.

While more and more applications are web-based in modern organizations, we will continue to have Windows-based applications for a long time. MSIX is closing the gaps in terms of compatibility with App-V and the ecosystem surrounding it is growing.

For those who have not yet explored MSIX, the author highly recommends it -- especially for admins and organizations that are reliant on App-V. The format's compatibility with existing technologies and its potential to streamline application management make it a valuable asset for any organization relying on Windows-based applications. It will also ease the adoption of services such as Azure Virtual Desktop which can also utilize MSIX for their app attach features.

Marius Sandbu is a cloud evangelist for Sopra Steria in Norway who mainly focuses on end-user computing and cloud-native technology.