What exactly is an Assembly in C# or .NET?

Question

Could you please explain what is an Assembly in C# or .NET?

1. Where does it begin and where does it end?
2. What important information should I know about

Answer 1

An Assembly is a collection of logical units. Logical units refer to the types and resources which are required to build an application and deploy them using the .Net framework. Basically, Assembly is a collection of Exe and DLLs. It is portable and executable.

Answer 2

Here's another explanation of the make up of .NET Assemblies, a mini-quote:

The .NET framework consists of the concepts of modules, assemblies, which both store metadata and manifest information. An assembly can contain multiple modules. Visual C# only ever creates one module which is turned into an assembly by the C# compiler (csc.exe), but an assembly can link many .NET modules together via the assembly linker (al.exe) command-line tool. For example each of your source code .cs files could be compiled into a module and linked together to form an assembly - an assembly is just a collection of modules and resources. One of these modules, however; must contain manifest metadata (see below) information for the assembly to be understood by the CLR.
....
Having created a new .exe or .dll inside VS.NET you see your file appear inside your bin folder. Opening it in notepad will give out gibberish, or even inside a hexadecimal editor without knowing the structure of the file, you need a tool like ildasm.exe or CFF explorer to make meaning from it. The structure of the assembly is as follows:

PE header
CLR header
CLR metadata
CLR
IL code
Native data

Answer 3

An assembly is the compiled output of your code, typically a DLL, but your EXE is also an assembly. It's the smallest unit of deployment for any .NET project.

The assembly typically contains .NET code in MSIL (Microsoft Intermediate language) that will be compiled to native code ("JITted" - compiled by the Just-In-Time compiler) the first time it is executed on a given machine. That compiled code will also be stored in the assembly and reused on subsequent calls.

The assembly can also contain resources like icons, bitmaps, string tables and so on. Furthermore, the assembly also contains metadata in the assembly manifest - information like version number, strong name, culture, referenced assemblies and so forth.

In 99% of your cases, one assembly equals a physical file on disk - the case of a multi-file assembly (one assembly, distributed across more than a single file) appears to be a rather odd-ball edge case which I've never encountered so far in my 5+ years of .NET development.

In a multifile assembly there would still be only one assembly manifest in a DLL or EXE and the MSIL code in multiple netmodule files.