Programming .NET Windows Applications

Assemblies

All files that comprise a .NET application are gathered into one or more assemblies. Assemblies are the basic unit of .NET programming. They appear to the user as dynamic link library (DLL) files or an executable (EXE) file. (DLLs contain classes and methods that are linked into an application at runtime as needed.)

Assemblies also contain versioning information. An assembly is the minimum unit for a single version of a piece of code. Multiple versions of the same code can run side by side in different applications, with no conflicts, by packaging the different versions into separate assemblies and specifying which version is allowed in the configuration files.

Assemblies can contain one or more files. The constituent files in an assembly are portable executable files such as EXEs or DLLs.

Microsoft Intermediate Language (MSIL)

When a .NET application is compiled into an executable file, that file does not contain machine code (unless it was compiled with the Managed C++ compiler), as is the case with most other language compilers. Instead, the compiler output is a language known as Microsoft Intermediate Language (MSIL), or IL for short. When the program is run, the .NET Framework calls a Just-In-Time (JIT) compiler to compile the IL into machine code, which is then executed. The JITed machine code is cached on the machine, so there is no need to recompile with every execution.

In theory, a program will produce the same IL code if written with any .NET compliant language. ...