Migration and Application Compatibility

Migrating to a new operating system poses certain unique challenges, primarily with the need to support legacy web applications. Organizations may have applications that were built for previous versions of Internet Explorer, such as Windows® Internet Explorer® 7 or Microsoft® Internet Explorer 6. These web applications may encounter compatibility issues with Internet Explorer 9. Additionally, Internet Explorer 6 does not natively run on Windows 7, and the option of running two versions of Internet Explorer simultaneously on Windows is not supported. For more information, see the Microsoft Knowledge Base article Running Multiple Versions of Internet Explorer on Single Operating System is Unsupported.

Many organizations are still relying on Internet Explorer 6 based web applications that have been built and customized over the past decade. Organizations planning to deploy Windows 7 need to have a comprehensive strategy and execution plan to migrate legacy web applications to Internet Explorer 9. This section of the deployment guide provides IT professionals a detailed overview of Internet Explorer 9 compatibility issues. It also discusses remediation strategies for migrating web applications, and provides an introduction to tools and processes.

To learn more about understanding and addressing Internet Explorer 9 application compatibility from a developer perspective, see Appendix 1: Internet Explorer 6 to Internet Explorer 9 Browser Changes.


If you are currently testing Internet Explorer 8 Microsoft recommends that you consider testing Internet Explorer 9 instead. If you are currently piloting or deploying Internet Explorer 8, consider adding a parallel project to pilot Internet Explorer 9 as part of your next critical deployment.

Understand the application compatibility challenge

Microsoft continues to evolve the browser with each new release, and now provides Internet Explorer 9 as the default browser in Windows 7. Internet Explorer 9 introduces numerous feature improvements, including an enhanced platform architecture that is designed to:

  • Make the web safer and faster for end users.

  • Make browsers easier to configure and manage for IT professionals.

  • Make it easier for web developers to create innovative content.

Some of these enhanced features needed entirely new rendering and scripting engines based on standards – the core elements used by Internet Explorer to display HTML/CSS content and script execution. It is this combination of architectural changes and platform enhancements based on standards that can potentially introduce application compatibility issues.

While Microsoft has worked hard to integrate backwards compatibility directly into the Internet Explorer 9 browser, there are some strategic design changes, web standards support, and security features which may require web applications built for Internet Explorer 6 or older to be upgraded in your organization.

Web standards and application compatibility

Before getting into the specifics of design change impacts, it is important to address web standards and their impact on application compatibility. Standards provide a common baseline of technologies, allowing users to select the web browser of their choice and be reasonably confident they will be able to use the websites they want. Standards also allow web designers and developers to create a single implementation of a website, with the expectation that everyone will be able to use it. By increasing choice and reducing fragmentation, everyone wins.

In the world of web browsers, standards are constantly evolving and browsers are continuously being updated to adopt these standards. Consequently, it is very important that IT professionals along with their development teams ensure web applications are compatible with current and emerging web standards and browsers. Doing so ensures the web applications and sites are compatible with new releases of the browser, and helps prevent many compatibility issues that might otherwise arise.

For additional information about planning for application compatibility and migration processes, see the following topics in the Windows section of the Microsoft TechNet library:

For additional information about application compatibility and migration scenarios for Internet Explorer 9, see the following topics in this Deployment Guide: