Traditionally, when a component or application is updated on a computer, the older version is removed and replaced with the newer version. If the new version is not compatible with the previous version, this usually breaks other applications that use the component or application. The .NET Framework provides support for side-by-side execution, which allows multiple versions of an assembly or application to be installed on the same computer concurrently. Since multiple versions can be installed simultaneously, managed applications can select which version to use without affecting other applications that use a different version.
In ASP.NET, applications are said to be running side-by-side when they are installed on the same computer, but use different versions of the .NET Framework. The following topics describe side-by-side support in ASP.NET and how to configure ASP.NET applications for side-by-side execution.