An Assembly is the smallest unit of deployment of a .net application. It can be a dll or an exe. It has mainly three types as follows,

1. Private Assembly

2. Public / Shared Assembly

3. Satellite Assembly

1. Private Assembly - A private assembly can be used by only a single application and not accessible for other applications. The dll or exe is generally stored in the application root folder.

2. Public / Shared Assembly - Public / Shared Assemblies are the assemblies that are accessible globally/shared across the machine to all the applications which are stored inside Global Assembly Cache (GAC), these can generally be found in the operating system folder like follows C:WindowsAssembly. For using the shared assemblies you need to register the assembly with a strong name in the GAC using gacutil.exe.

most common assemblies contained in the Global Assembly Cache,

1. System.dll
2. System.Configuration.dll
3. System.Data.dll
4. System.Drawing.dll
5. System.Web.dll
6. System.Web.Services.dll
7. System.Xml.dll
8. Mscorlib.dll

3. Satellite Assembly - satellite assemblies are useful while creating multilingual applications. Using satellite assemblies, localizable resources can be placed for different languages in different assemblies.