Chapter 21: Assemblies

Overview

By now, you’ve probably developed some programs in .NET, so you’ve seen the modules produced by the .NET compilers, which have file extensions of .dll or .exe. Most .NET modules are DLLs, including class libraries and those that serve as code-behind for ASP.NET. Windows applications, console applications, and Windows Services are examples of .NET modules that are executables and thus have an extension of .exe.

These .NET-compiled modules, both DLLs and EXEs, are referred to as assemblies. Assemblies are the unit of deployment in .NET, containing both compiled code and metadata that is needed by the .NET common language runtime (CLR) to run the code. Metadata includes information such as the code’s identity and version, dependencies on other assemblies, and a list of types and resources exposed by the assembly.

Basic development in .NET doesn’t require you to know any more than that. However, as your applications become more complex, and as you begin considering such issues as deployment and maintenance of your code, you need to understand more about assemblies. This chapter addresses that need, including the following:

• What assemblies are and how they are used

• The general structure of an assembly

• How assemblies can be versioned

• The global application cache (GAC), including how and when to use it

• How assemblies are located and loaded by the CLR

After you are familiar with these essentials, Chapter 22 uses this information to discuss deployment in depth.