.NET Framework vs .NET Core vs .NET 5+ — the history explained — .NET Internals

The .NET Framework, .NET Core, and .NET 5+ represent three distinct versions of the popular .NET software development platform. The history of these versions spans from 2002 to 2022, with .NET 5+ being released in 2020. The .NET Framework was initially released for the Windows operating system only, while .NET Core brought multi-platform support, including Windows, Linux, and macOS. As of 2022, .NET 5+ supports Windows, Linux, macOS, mobile (MAUI), WebAssembly, and single-file executables.

The .NET Framework has been maintained for machine-wide installation, as part of Windows, and also as a side-by-side deployment. On the other hand, .NET Core offers same deployment mode along with self-contained deployments and Native AOT (Ahead-of-Time) compilation for reduced startup time. .NET 5+ takes it a step further by offering single-file executables, Native AOT, and improved performance.

ASP.NET, a web application framework, evolved alongside these versions. ASP.NET Web Forms, MVC 5, and ASP.NET Web API 2 were used with .NET Framework, while ASP.NET Core, ASP.NET Core MVC, and ASP.NET Core Web API are the corresponding frameworks for .NET Core and .NET 5+. Performance-wise, .NET Framework offers good performance; .NET Core is much faster, and .NET 5+ is the fastest, with performance improvements in each release.

The Common Language Runtime (CLR) serves as the execution engine for .NET, handling tasks such as loading assemblies, verifying type safety, JIT-compiling Intermediate Language (IL) code to native machine code, memory management using the garbage collector, exception handling, thread and synchronization management, and providing interop with native code and debugging/profiling services. Code executed under the CLR is considered "managed code."

Two key concepts in .NET are the Common Type System (CTS) and the Common Language Specification (CLS). CTS defines how types are declared and used across .NET languages like C# and VB.NET, ensuring a shared type system. CLS is a subset of CTS rules that every .NET language supports, allowing CLS-compliant libraries to be used across different languages without compatibility issues.