What is an assembly in .NET Framework?
An assembly is the primary building block of a .NET Framework application. It is a collection of functionality that is built, versioned, and deployed as a single implementation unit (as one or more files). All managed types and resources are marked either as accessible only within their implementation unit, or as accessible by code outside that unit.
Assemblies are self-describing by means of their manifest, which is an integral part of every assembly. The manifest:
What is assembly manifest?
Every assembly, whether static or dynamic, contains a collection of data that describes how the elements in the assembly relate to each other. The assembly manifest contains this assembly metadata. An assembly manifest contains all the metadata needed to specify the assembly's version requirements and security identity, and all metadata needed to define the scope of the assembly and resolve references to resources and classes. The assembly manifest can be stored in either a PE file (an .exe or .dll) with Microsoft intermediate language (MSIL) code or in a standalone PE file that contains only assembly manifest information.
For an assembly with one associated file, the manifest is incorporated into the PE file to form a single-file assembly. You can create a multi-file assembly with a standalone manifest file or with the manifest incorporated into one of the PE files in the assembly.
Explain the information stored in assembly manifest.
Assembly manifest contains the following information:
Assembly name -A text string specifying the assembly's name.
Version number- A major and minor version number, and a revision and build number. The common language runtime uses these numbers to enforce version policy.
Culture- Information on the culture or language the assembly supports. This information should be used only to designate an assembly as a satellite assembly containing culture- or language-specific information. (An assembly with culture information is automatically assumed to be a satellite assembly.)
Strong name information- The public key from the publisher if the assembly has been given a strong name.
List of all files in the assembly- A hash of each file contained in the assembly and a file name. Note that all files that make up the assembly must be in the same directory as the file containing the assembly manifest.
Type reference information -Information used by the runtime to map a type reference to the file that contains its declaration and implementation. This is used for types that are exported from the assembly.
Information on referenced assemblies -A list of other assemblies that are statically referenced by the assembly. Each reference includes the dependent assembly's name, assembly metadata (version, culture, operating system, and so on), and public key, if the assembly is strong named.
You can add or change some information in the assembly manifest by using assembly attributes in your code. You can change version information and informational attributes, including Trademark, Copyright, Product, Company, and Informational Version. Every assembly, whether static or dynamic, contains a collection of data that describes how the elements in the assembly relate to each other. The assembly manifest contains this assembly metadata. An assembly manifest contains all the metadata needed to specify the assembly's version requirements and security identity, and all metadata needed to define the scope of the assembly and resolve references to resources and classes. The assembly manifest can be stored in either a PE file (an .exe or .dll) with Microsoft intermediate language (MSIL) code or in a standalone PE file that contains only assembly manifest information. For an assembly with one associated file, the manifest is incorporated into the PE file to form a single-file assembly. You can create a multi-file assembly with a standalone manifest file or with the manifest incorporated into one of the PE files in the assembly.
What are the functions performed by the assembly manifest?
Each assembly's manifest performs the following functions:
* Enumerates the files that make up the assembly.
* Governs how references to the assembly's types and resources map to the files that contain their declarations and implementations.
# Enumerates other assemblies on which the assembly depends.
# Provides a level of indirection between consumers of the assembly and the assembly's implementation details.
# Renders the assembly self-describing.
What is GAC (Global Assembly Cache)?
Each computer where the common language runtime is installed has a machine-wide code cache called the global assembly cache that stores assemblies specifically designated to be shared by several applications on the computer.
You should share assemblies by installing them into the global assembly cache only when you need to. As a general guideline, keep assembly dependencies private, and locate assemblies in the application directory unless sharing an assembly is explicitly required. In addition, it is not necessary to install assemblies into the global assembly cache to make them accessible to COM interop or unmanaged code.
Assemblies deployed in the global assembly cache must have a strong name. When an assembly is added to the global assembly cache, integrity checks are performed on all files that make up the assembly.
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