Without these reference assemblies, Visual Studio would assume you are targeting the highest installed framework (e.g., .NET 4.8), leading to builds that fail on machines that only have .NET 4.0 installed.
is a set of reference assemblies that allows developers to build applications for specific .NET Framework versions without requiring that specific version to be the primary runtime on the development machine. Super User Reference Assemblies
Let's break down the name:
#if NET40 // Work around a bug in .NET 4.0's ConcurrentDictionary UseLegacyFallback(); #else UseModernAPI(); #endif
This guide outlines the purpose, installation, and troubleshooting of the Microsoft .NET Framework 4 Multi-Targeting Pack microsoft .net framework 4 multi targeting pack
Once you have the .NET Framework 4 Multi-Targeting Pack installed, use these strategies to avoid pain.
The .NET Framework 4 Multi-Targeting Pack is a quiet hero of the 2010s Windows development era. It decoupled from build environments , allowing teams to modernize tooling without rewriting history. Even today, in .NET 8 projects, you’ll find echoes of its design in the TargetFrameworks property (plural) and FrameworkReference items. : Directives and build targets for MSBuild, allowing
: Directives and build targets for MSBuild, allowing the underlying build engine to correctly package, validate, and link code targeted at a specific sub-version (such as .NET 4.0, 4.5.1, or 4.6). Multi-Targeting vs. Runtime: The Key Distinction Multi-Targeting Pack / Developer Pack Runtime / Redistributable Pack Primary Audience Software Developers / Engineers End Users / Consumers Purpose Building and compiling applications Executing compiled applications Contents Reference assemblies, XML IntelliSense, MSBuild targets IL binaries, CLR (Common Language Runtime), physical DLLs Deployment Installed exclusively on development machines Installed on client machines and production servers Why Do Modern Legacy Environments Need It?
Leo watched as a new folder bloomed inside C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.0 . Files appeared: System.dll , System.Core.dll , System.Data.dll . They were empty shells—no actual code inside. Just maps. Just blueprints. Just promises. Just maps. Just blueprints. Just promises.
Needed on the machine where the application will run, as explained in the Microsoft .NET Framework 4.5.1 Developer Pack guide .