Side-by-Side Execution
.NET Framework 3.5
Side-by-side execution is the ability to install multiple versions of code so that an application can choose which version of the common language runtime or of a component it uses. Subsequent installations of other versions of the runtime, an application, or a component will not affect applications already installed.
This section describes side-by-side execution, how the runtime determines which version of the .NET Framework assemblies to load, and how to design software to take advantage of side-by-side execution.