Dynamic-Link Libraries

Dynamic linking provides a mechanism for linking applications to libraries of functions at run time. The libraries reside in their own executable files and are not copied into an application's executable file as with static linking. These libraries are "dynamically linked" because they are linked to an application when it is loaded and executed rather than when it is linked. When an application uses a DLL, the operating system loads the DLL into memory, resolves references to functions in the DLL so that they can be called by the application, and unloads the DLL when it is no longer needed. Dynamic linking can be performed explicitly by applications or implicitly by the operating system.

DLLs are designed to provide resources to applications. Many applications can use the code in a DLL, meaning that only one copy of the code is resident in the system. Also, it is possible to update a DLL without changing applications that use the DLL, as long as the interface to the functions in the DLL does not change.

Software developers can extend the Windows environment by creating a DLL that contains routines for performing operations and then making the DLL available to other Windows-based applications (in addition to internal Windows routines). DLLs most often appear as files with a .DLL filename extension; however, they may also have an .EXE or other filename extension.

For more information about dynamic-link libraries, see Dynamic-Link Libraries.

Windows 95/98 supports 32-bit DLLs as well as 16-bit DLLs that were written for Windows version 3.x. For a discussion of the issues involved in mixing 16- and 32-bit components in the Windows 95/98 environment, see Thunk Compiler.