Explain about Assemblies, native assemblies, and the Global Assembly Cache

The primary unit of deployment is the assembly. The assembly is used by the .NET CLR as the smallest unit of deployment; version control; security; type grouping and code reuse. An assembly will consist of a manifest and one or more modules or files.

It can be defined as a logical DLL that contains a manifest, type metadata, MSIL and resources. Assemblies can be application private or shared. Private assemblies are restricted to use in a single application whereas shared assemblies can be used across applications. Private applications also reside within the application folder while shared assemblies reside in the common area-- GAC(Global Assembly Cache). They must have a globally unique name.

The assembly is identified by the manifest. It defines security requirements, lists other interdependent assemblies and all the types and resources exposed by the assembly. Localized resources exposed by assemblies and targeted by the application contain a default culture (language, currency, date/time format etc).

The manifest contains several sections. Identity, Referenced Assemblies, file list and Custom Attributes are some of the important sections of the manifest. The Identity section as the name suggests, identifies the assembly. It contains a .assembly directive.

The version directive specifies the version of the assembly, so that the CLR identifies the different versions of an application. The Identity section contains a strong name for shared assemblies and a public/private encryption key is used to distinguish between assemblies of the same name. The Identity section also optionally contains the Culture which defines the country and language of the assembly target.

The .locale directive is used for this purpose and the Culture-Neutral assemblies can be used by any assembly.

The Referenced Assemblies section of the manifest provides a reference to all the assemblies used in an application.