An assembly is a runtime unit consisting of types and other resources. All types in an assembly have the same version

Versioning file system

A versioning file system is any computer file system which allows a computer file to exist in several versions at the same time. Thus it is a form of revision control. Most common versioning file systems keep a number of old copies of the file. Some limit the number of changes per minute or per...

 number.

Often, one assembly has only one namespace and is used by one program. But it can span over several namespaces

Namespace (computer science)

A namespace is an abstract container or environment created to hold a logical grouping of unique identifiers or symbols . An identifier defined in a namespace is associated only with that namespace. The same identifier can be independently defined in multiple namespaces...

. Also, one namespace can spread over several assemblies. In large designs, an assembly may consist of multiple files that are held together by a manifest (i.e. a table of contents).

In C#, an assembly is the smallest deployment

Deployment diagram

A deployment diagram in the Unified Modeling Language models the physical deployment of artifacts on nodes. To describe a web site, for example, a deployment diagram would show what hardware components exist , what software components run on each node , and how...

 unit used, and is a component in .NET

.NET

.NET may refer to:* .NET Framework, a software framework by Microsoft* .net, a top-level domain* .net * .NET Passport, an old name for Windows Live ID* .NET Messenger Service...

. In Java

Java (programming language)

Java is a programming language originally developed by James Gosling at Sun Microsystems and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities...

, it is a JAR file.

Creation of an assembly

Every compilation creates either an assembly or a module in C#. It is possible to add other modules with the assembly linker (al). A speciality of Java is to create a *.class file for each class, which is not the case in C#. The creation can be activated by compiler switches, like csc /addmodule:Y.netmodule A.cs that yields a new A.exe with Y added to this assembly.