What is Common Language Runtime (CLR)

Common Language Runtime (CLR)

The Common Language Runtime (CLR) is a core component of .NET Framework that manages the execution and the lifecycle of all .NET applications (code). It provides various services, including automatic memory management, exception handling, security, and type safety. When a .NET application is compiled, it generates an intermediate language code called Common Intermediate Language (CIL). The CLR is responsible for translating this CIL into machine code and managing the execution of the resulting program. The CLR also provides a platform for interoperability between different programming languages that target the .NET Framework. This means that a program written in one .NET language can easily use libraries written in another .NET language. Overall, the CLR is an essential component of the .NET Framework that enables developers to create robust, secure, and interoperable applications.

Key attributes of .NET CLR 

  • As part of the Microsoft .NET Framework, the Common Language Runtime (CLR) is the programming (Virtual Machine component) that manages the execution of programs written in any language that uses the .NET Framework, for example, C#, VB.Net, F# and so on.
  • Programmers write code in any language, including VB.Net, C#, and F#, when they compile their programs into an intermediate form of code called CLI in a portable execution file (PE) that can be managed and used by the CLR. Then the CLR converts it into machine code to be will be executed by the processor.
  • The information about the environment, programming language, its version, and what class libraries will be used for this code are stored as metadata with the compiler that tells the CLR how to handle this code.
  • The CLR allows an instance of a class written in one language to call a method of the class written in another language.

Got it? Let's try to look at the process of a C# application in the below diagram.

CLR Diagram

As you can see from the above diagram, the CLR provides several services.

Functions of .NET CLR

The key functions of the .NET CLR include the following:

  • Convert code into CLI
  • Exception handling
  • Type safety
  • Memory management (using the Garbage Collector)
  • Security
  • Improved performance
  • Language independency
  • Platform independency
  • Architecture independency

Components of .NET CLR

The key components of CLR include the following:

  • Class Loader - Used to load all classes at run time.
  • MSIL to Native code - The Just In Time (JTI) compiler will convert MSIL code into native code.
  • Code Manager - It manages the code at run time.
  • Garbage Collector - It manages the memory. Collect all unused objects and deallocate them to reduce memory.
  • Thread Support - It supports the multithreading of our application.
  • Exception Handler - It handles exceptions at run time.

Benefits of .NET CLR

The runtime provides the following benefits:

  • Performance improvements.
  • The ability to easily use components developed in other languages.
  • A class library provides extensible types.
  • Language features such as inheritance, interfaces, and overloading for object-oriented programming.
  • Support for explicit free threading that allows the creation of multithreaded, scalable applications.
  • Support for structured exception handling.
  • Support for custom attributes.
  • Garbage collection.
  • Use of delegates instead of function pointers for increased type safety and security.


In this article, I discussed the basics of .NET CLR, its components, work, and benefits. While this article was written based on earlier versions of .NET, the current CLR version is 5. Going forward, the .NET Framework and .NET Core will become one as .NET 5. I highly recommend reading this article: Future of .NET

Similar Articles