common language runtime is the execution engine for .NET Framework applications. 
Provideing

• Enforcement of code access security 
• Exception handling 
• Interoperation  COM objects, and pre-existing DLLs 
• Automation of object layout 
• Code management (loading and execution) 
• Application memory isolation 
• type safety 
• Convert IL to native code 
• Access to metadata 
• memory management  

  What is the common type system (CTS)? 

  What is the Common Language Specification (CLS)? 

  What is the Microsoft Intermediate Language (MSIL)? 

  What is managed code and managed data?