What is a CLR?

Its an abbreviation for Common Language Runtime and its the heart and brain of the .NET framework.
-->The common language runtime is the execution engine for .NET Framework applications.

Following are the responsibilities of CLR
• Garbage Collection: - CLR automatically manages memory thus eliminating
memory leaks. When objects are not referred, GC automatically releases those
memories thus providing efficient memory management.
• Code Access Security: - CAS grants rights to program depending on the security
configuration of the machine. Example the program has rights to edit or create a
new file but the security configuration of machine does not allow the program to
delete a file. CAS will take care that the code runs under the environment of
machines security configuration.
• Type Safty
• Thread Management
• Exception Handling
• IL(Intermediate language) - To - native translators and optimizer’s:- CLR uses JIT, compiles the IL code to machine code, and then executes. CLR also determines depending on platform what is optimized way of running the IL code.

MSIL : (Microsoft Intermediate language) or IL(Intermediate Language) is machine independent code generated by .NET framework after the compilation of program written in any language.