A DLL (dynamic link library), was made by Microsoft to implement the concept of shared libraries in the Microsoft Windows operating systems and OS / 2. These libraries usually have the extensions DLL, OCX (for libraries containing ActiveX controls), or DRV (for legacy system drivers).
The file formats for DLLs are the same as the executable files for Windows. Just as the executable (EXE), DLLs can contain code, data, and resources (icons, fonts, cursors, etc.) in any combination.