Common Language Runtime (CLR)

You have learned that the compiler produces CIL (packaged inside an assembly) from your source code. But who actually executes this CIL? The answer: the "Common Language Runtime", or CLR for short.

The CLR is a program that runs on your operating system and reads CIL. Using a technique called "Just-In-Time" (JIT) compilation, it translates the CIL into the machine language that your specific device's processor understands — right as the program runs, whether that's a Windows PC, a Mac, or a Linux server.

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The CLR uses ____-In-Time compilation to translate CIL into machine language as the program runs.

Beyond translating CIL, the CLR also manages important background tasks for your program: it automatically frees up memory that is no longer needed (a process called "garbage collection"), enforces C#'s strong typing rules, and handles errors that occur while the program is running.

The CLR automatically manages memory for a running C# program through garbage collection.

The complete process looks like this: you write Program.cs (source code). The Roslyn compiler translates it into an assembly containing CIL. The CLR reads that assembly and executes it, JIT-compiling the CIL into machine code for your device along the way.

What is the main job of the Common Language Runtime (CLR)?