All 19 CLR & Runtime questions
More in CLR & Runtime
What is the Common Type System (CTS), and how does it enable interoperability between different .NET languages? What is the relationship between the CLR and the .NET class library (BCL - Base Class Library)? What does the `unsafe` keyword and pointer usage in C# allow, and why would a developer opt into it? What is the difference between the CLR's Server GC and Workstation GC modes, and how do you choose between them? What is tiered compilation, and how does it balance fast startup with peak execution performance? What is boxing and unboxing, and what performance cost does it incur? How does the CLR handle exceptions at a low level, and what is the performance implication of throwing exceptions frequently? How does the CLR ensure type safety and memory safety, and what categories of bugs does this prevent compared to unmanaged languages like C++? How does Span<T> improve performance for buffer and array manipulation compared to traditional array slicing? How does the CLR's Dynamic Profile-Guided Optimization (Dynamic PGO) improve JIT-compiled code quality at runtime?
Advertisement
Back to results for “.NET vs .NET Framework”
.NET › CLR & Runtime

What is the AppDomain concept in .NET Framework, and why was it removed from modern .NET?

Intermediate

Answer

AppDomains in .NET Framework provided isolated execution boundaries within a single process, allowing multiple applications (or plugins) to run with separate loaded assemblies, security contexts, and the ability to unload one without affecting others -- but with significant overhead from cross-domain marshaling for any communication. Modern .NET removed AppDomains (only a single default domain exists) in favor of the much lighter-weight AssemblyLoadContext for assembly isolation and Process-level isolation (containers, separate processes) for stronger security/fault boundaries, reflecting a simpler and more performant design given modern deployment practices.
// .NET Framework (legacy): AppDomain-based isolation
AppDomain domain = AppDomain.CreateDomain("PluginDomain");
// .NET Framework only -- not available in modern .NET

// Modern .NET equivalent: AssemblyLoadContext
var alc = new AssemblyLoadContext("PluginContext", isCollectible: true);
Real-world example A legacy Framework application relying on AppDomain-based plugin isolation must be redesigned around AssemblyLoadContext (for assembly-level isolation) or separate worker processes (for full fault isolation) when migrating to modern .NET.

Common follow-ups: What cross-domain communication overhead did AppDomains impose?;Why is process isolation now preferred for strong security boundaries instead?

.NET vs .NET Framework;Assemblies & NuGet
All 19 CLR & Runtime questions