Side-by-side Execution

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.

Benefits of Side-by-Side Execution
Prior to Microsoft Windows XP and the .NET Framework, DLL conflicts occurred because applications were unable to distinguish between incompatible versions of the same code. Type information contained in a DLL was bound only to a file name. An application had no way of knowing if the types contained in a DLL were the same types that the application was built with. As a result, a new version of a component could overwrite an older version and break applications.

Side-by-side execution and the .NET Framework provide the following features to eliminate DLL conflicts:

•Strong-named assemblies.Side-by-side execution uses strong-named assemblies to bind type information to a specific version of an assembly. This prevents an application or component from binding to an invalid version of an assembly. Strong-named assemblies also allow multiple versions of a file to exist on the same computer and to be used by applications.
•Version-aware code storage.The .NET Framework provides version-aware code storage in the global assembly cache. The global assembly cache is a computer-wide code cache present on all computers with the .NET Framework installed. It stores assemblies based on version, culture, and publisher information, and supports multiple versions of components and applications.
•Isolation. Using the .NET Framework, you can create applications and components that execute in isolation, an essential component of side-by-side execution. Isolation involves being aware of the resources you are using and sharing resources with confidence among multiple versions of an application or component. Isolation also includes storing files in a version-specific way.