We can say that assembly is a combination of single-file or multiple files in ASP .NET. The assembly which contains more then one file is dynamic link library (DLL) or we can also say it's an EXE file. In ASP.NET assembly contains metadata that is pronounced as assembly manifest. This manifest of assembly contains data about the assembly versioning, AuthorName, Security, Token Key etc that's makes assembly popular and secure.
We can also say it's a big advantage of assembly and another big advantage of using ASP.NET Assemblies is that programmer need not to create applications without interfering with other applications on the system its means assembly requirement in one application can not harm another application that using that assembly because assembly in one application is not applied to another application.
But one assembly can be shared with many applications. In asp dot net 2003 assembly is placed in Bin directory of the application that uses it. This advantage make assembly so popluar because this is one of the drawback in of DLL in the past.
In past, developers need to share libraries of code through DLL. And when same dll is needed in applications then users have to register that DLL on to the machine. One of main thing in ASP NET is that the assembly is created by default when we build our application or DLL. We can also check the details of the manifest of the assembly by using classes located in the System.Reflection namespace. We can create two types of assemblies in ASP .NET.
There are many advantages of assembly some of them are as follows:
(1) Increased performance.
(2) Better code management and encapsulation.
(3) Introduces the n-tier concepts and business logic.
In asp dot net System namespace and other namespaces like it ie System.Data, System.Web are also pre-built assemblies that have been provided in the dot net framework to us by Microsoft.