Just in time for Back to School specials, Juice contributor Vijay.Raj provides this concise overview to Assemblies.
Time to bust out the books and brush up.
The assembly which is used only by a single application is called as private assembly. Suppose you created a DLL which encapsulates your business logic. This DLL will be used by your client application only and not by any other application. In order to run the application properly your DLL must reside in the same folder in which the client application is installed. Thus the assembly is private to your application.
Suppose that you are creating a general purpose DLL which provides functionality which will be used by variety of applications. Now, instead of each client application having its own copy of DLL you can place the DLL in 'global assembly cache'. Such assemblies are called as shared assemblies.
Global assembly cache is nothing but a special disk folder where all the shared assemblies will be kept. It is located under <drive>:\WinNT\Assembly folder.
As stated earlier most of the assemblies are private. Hence each client application refers assemblies from its own installation folder. So, even though there are multiple versions of same assembly they will not conflict with each other. Consider following example:
Now consider the case when you develop assembly that is shared one. In this case it is important to know how assemblies are versioned. All assemblies has a version number in the form: major.minor.build.revision
If you change the original assembly the changed version will be considered compatible with existing one if the major and minor versions of both the assemblies match.
When the client application requests assembly the requested version number is matched against available versions and the version matching major and minor version numbers and having most latest build and revision number are supplied.