Lesson 1 / 26

What .NET Is

Tell apart the SDK, the runtime and .NET Framework, and explain why modern .NET is cross-platform.

SDK vs runtime

The SDK has the compiler and the dotnet CLI for building apps. The runtime only runs finished apps. Developers install the SDK; servers can run with just the runtime.

From source to running app

Your C# is compiled to intermediate language, then the runtime turns it into machine code when the app runs.

Four connected stages from C# source to a running process.
Figure 1.1 — Source, compile, runtime, running app.

A kitchen analogy

The SDK is the full kitchen where you cook. The runtime is the dining table where the finished dish is served. A restaurant customer needs only the table.

Do not confuse the names

".NET Framework" is the older Windows-only product. ".NET Core" became plain ".NET" from version 5 onward. Tutorials for "ASP.NET" (System.Web) often do not apply to modern ASP.NET Core.

Quick check: Which piece must a build machine have to compile C# apps?

  • Only the runtime
  • Only a web browser
  • The .NET SDK
  • .NET Framework 4.8
Answer

The .NET SDK — The SDK includes the compiler and CLI. The runtime alone can run apps but not build them.