Dynamic Link Library (DLL) files are an essential part of the Windows operating system. Although they are ubiquitous, most PC users neither know nor care what these files do. Nonetheless, a little understanding of the role that DLL files play can make the computer a little less of a mystery box.
Only programmers and computer technicians need to know any of the gory details of the structure and function of a DLL, but these files are so important that all of us should know a few simple facts about them. Here is some information for the non-technical PC user
COMDLG32.DLL Controls the dialog boxes GDI32.DLL Contains numerous functions for drawing graphics, displaying text, and managing fonts
KERNEL32.DLL Contains hundreds of functions for the management of memory and various processes
Contains numerous user interface functions. Involved in the creation of program windows and their interactions with each other
Regular DLL's can export only functions, variables or resources. These can be loaded by any Win32 environment (e.g. VB 5) Regular DLLs are generally larger in size. When you build a regular DLL, you may choose a static link (in this case MFC library code is copied to your DLL) and dynamic (in this case you would need MFC DLLs to be presented on the target machine)
Along with functions, variables and resources Extension DLL's can export Classes as well. It supports a C++ interface, i.e. can export whole C++ classes and the client may construct objects from them. Extension DLL dynamically links to MFC DLLs (those which name starts with MFC??.DLL) Extension DLL is usually small (simple extension DLL might be around 10K).
To determine the version number, company name or other information about a file: