The building blocks of the .NET framework are generally 
defined as assemblies.

Its main deployment unit in .net framework. It provides the 
total info to the run time while running the application.

Either Excutable File (EXE) or Class Library File(DLL) 
which which having Mainfeast data,IL Code. Using This 
Assembly Concept Microsoft Acchieve PlatForm Independency .

Assemblies are the building blocks of .NET Framework 
applications; they form the fundamental unit of deployment, 
version control, reuse, activation scoping, and security 
permissions. An assembly is a collection of types and 
resources that are built to work together and form a 
logical unit of functionality. An assembly provides the 
common language runtime withthe information it needs to be 
aware of type implementations. To the runtime, a type does 
not exist outside the context of an assembly. Assemblies 
are a fundamental part of programming withthe .NET 
Framework. An assembly performs the following functions: o 
It contains code that the common language runtime executes. 
Microsoft intermediate language (MSIL) code in a portable 
executable (PE) file will not be executed if it does not 
have an associated assembly manifest. Note that each 
assembly can have only one entry point (that 
is,DllMain,WinMain, orMain). o It forms asecurity boundary. 
An assembly is the unit at which permissions are requested 
and granted. o It forms atype boundary. Every type?s 
identity includes the name of the assembly in which it 
resides. A type called MyType loaded in the scope of one 
assembly is not the same as a type called MyType loaded in 
the scope of another assembly. o It forms areference scope 
boundary. The assembly?s manifest contains assembly 
metadata that is used for resolving types and satisfying 
resource requests. It specifies the types and resources 
that are exposed outside the assembly. The manifest also 
enumerates other assemblies on which it depends. o It forms 
aversion boundary. The assembly is the smallest versionable 
unit in the common language runtime; all types and 
resources in the same assembly are versioned as a unit. The 
assembly?s manifest describes the version dependencies you 
specify for any dependent assemblies. o It forms a 
deployment unit. When an application starts, only the 
assemblies that the application initially calls must be 
present. Other assemblies, such as localization resources 
or assemblies containing utility classes, can be retrieved 
on demand. This allows applications to be kept simple and 
thin when first downloaded. o It is the unit at which side-
by-side execution is supported. Assemblies can be static or 
dynamic. Static assemblies can include .NET Framework types 
(interfaces and classes), as well as resources for the 
assembly (bitmaps, JPEG files, resource files, and so on). 
Static assemblies are stored on disk in PE files. You can 
also use the .NET Framework to create dynamic assemblies, 
which are run directly from memory and are not saved to 
disk before execution. You can save dynamic assemblies to 
disk after they have executed. There are several ways to 
create assemblies. You can use development tools, such as 
Visual Studio .NET, that you have used in the past to 
create .dll or .exe files. You can use tools provided in 
the .NET Framework SDK to create assemblies withmodules 
created in other development environments. You can also use 
common language runtime APIs, such as Reflection.Emit, to 
create dynamic assemblies

> Assembly is primary buliding block in .net 
> Assembly  is smallest deployment unit in any application 
> Assembly is grouping of phishcal unit which contain 
information about matadata and mainfest.

assembly is the collection of dll and exe files.
this assembly wil create in CLR
this clr wil give run time environment for .net applications