.NET Framework Components

The .NET Framework is simply a collection of two components

1. FCL (.NET Framework Class Library)
2. CLR (Common Language Runtime)

You can see the .NET Framework Architecture in the following diagram.

1.  .NET Framework Class Library (FCL)

• The  .NET  Framework  class  library  contains  the  necessary  library  classes  that  are needed  for  development  of  different  types  of  .NET  applications  like  Console applications,  Windows  applications,  Windows  services,  ASP.NET  Web  sites,  ASP.NET Web  Services,  Windows  Communication  Foundation  (WCF)  applications  and  Windows Presentation Foundation (WPF) applications.
• The library‘s classes are organized using a hierarchy of namespaces.
• A namespace is nothing but a collection of classes. 
• For  example,  all  the  classes  for  performing  I/O  operations  are  located  in  the System.IO namespace.
• All  the  types  (structures  and  classes)  are  commonly  available  for  all  the  .NET languages. This concept can be called as ―CTS (Common Type System).

( i ). Naming Convention :

We have to follow these naming conventions for good practice of programming:

For Namespace, Classes, Structures and Methods:

• Each world in the name space should be started with upper case character.
• Ex: WebControls, Threading, OleDbClient, InitializeComponent() etc.

For Variables and objects:

• This is programmer‘s choice. You can maintain all the characters in lower case (or) you can also maintain the naming convention recommended for namespaces.
• Ex: i, abc, Abc, AbcXyz etc

( ii ). The .NET Framework Class Library (FCL) Architecture :

The .NET Framework Class Library contains the following namespaces.

Note:  A  namespace is a collection of few classes or namespaces.The inner namespaces, contained by another namespace is called as sub namespace. The most frequently used namespaces of FCL are listed here.

2. Common Language Run Time (CLR)

• The  Common  Language  Runtime  (CLR)  is  the  agent  that  manages  your  .NET applications  at  execution  time.  In  other  words,  CLR  is  the  completely  responsible component of .NET Framework that is responsible to manage the .NET applications at run time.
• In  other  words,  The  Common  Language  Runtime  (CLR)  is  the  virtual  machine  in  the .NET Framework.
• It  provides  core  services  such  as  memory  management,  thread  management, exception handling, security and resource management.
• A  .NET  application  is  compiled  into  a  ―bytecode‖  format  known  as  MSIL  (Microsoft Intermediate  Language).  The  MSIL  bytecode  allows  .NET  applications  to  be  portable (at least theoretically) to other platforms because the application is compiled to native code only during runtime.
• During  execution,  the  CLR‘s  JIT  (just  -  in  -  time)  compiles  the  bytecode  into  the processor‘s native code and executes the application.

( i ). Assemblies and Microsoft Intermediate Language (MSIL) :

• In .NET, when an application is compiled, into a bytecode called MSIL. That MSIL code is  stored  in  an  assembly.  The  assembly  is  contained  in  one  or  more  PE  (portable executable) files and may end with an EXE or DLL extension.
• The assembly contents are:

            -> Byte code — The code in MSIL language.

            -> Security  Information  —  Information  about  the  users  /  user  types,  who  can 

                 access the assembly.

            -> Manifest  —  Information  about  the  assembly,  such  as  identification,  name, 

                 version, and so on.

            -> Versioning — The version number of an assembly.

            -> Metadata — Information that describes the types and methods of the assembly.

( ii). Types of Assemblies

• Private Assemblies:  The private assemblies are simple types. An assembly that can be used only within a software application is called as Private assembly.  This type of assemblies contains ―.exe file extension.
• Shared  Assemblies:  An  assembly  that  can  be  used  by  one  or  more  software applications  is  called  as  Shared  Assemblies.  This  type  of  assemblies  contains  .dll(dynamic linking library) file extension.

Example:

                 To get a better idea of a MSIL file and its content, take a look at the following example, which has two console applications. One is written in C# and the other is written i n VB.NET.

The  following  C#  code  displays  the  “Hello,  World”  message  in  the console window :

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

namespace HelloWorldCS

  {

   class Program

    {

      static void Main(string[] args)

      {

        Console.WriteLine(―Hello, World!‖);

        Console.ReadLine();

       }

      }

    }

The Main method of the C# MSIL looks like this:

.method private hidebysig static void Main(string[] args) cil managed

 {

   .entrypoint

   // Code size 19 (0x13)

     .maxstack 8

     IL_0000: nop

     IL_0001: ldstr ―Hello, World!‖

     IL_0006: call void [mscorlib]System.Console::WriteLine(string)

     IL_000b: nop

     IL_000c: call string [mscorlib]System.Console::ReadLine()

     IL_0011: pop

     IL_0012: ret

 } // end of method Program::Main

The important thing to note here is that regardless of the language you use to develop your .NET applications, all .NET applications are compiled to the MSIL bytecode as this example shows.

Note:  MSIL  can  also  be  called  as  IL  (Intermediate  Language)  and  CIL  (Common  Intermediate 

            Language).

The RTE (Run Time Environment) of a .NET Application

Common Language Runtime Video

CLR Video 2    Click Here

Role of CLR Video  Click Here