What is the difference between COM DLL, Registry and Normal DLL?

Dll stand for Dynamic Link Library. These files are used by applications to perform their specified tasks. In broad sense we can say that, these are the common files used by many applications in order to minimize ammount of disk space they consume on your hard drive and to improve memory performance.

Registry is an executable file which contains all the information about your Windows OS. This is not shared by number of applications. Every application have their own registry entries.

COM (Component Object Model) is the component model based on the object oriented design, which means that the components represented by the COM component exists in the form of classes and objects implementing a standard specification defined by COM. COM components can be used by any program running on Windows Operating System; be it is written with VB, C++, Java or even some .NET compliant language like C# and VB.NET.