Definition and Explanation of a .DLL file

A dynamic-link library (DLL) file is an executable file that allows programs to share code and other resources necessary to perform particular tasks. Microsoft Windows provides DLL files that contain functions and resources that allow Windows-based programs to operate in the Windows environment.

DLLs most often appear as files with a .DLL extension; however, they may also have an .EXE or other extension. For example, Shell.dll provides the Object Linking and Embedding (OLE) drag and drop routines that Windows and other programs use.

Kernel.exe, User.exe and Gdi.exe are examples of DLLs with .EXE extensions. They provide code, data or routines to programs running in the Windows operating system. For example, one of these files provides the "CreateWindow" function that programs use when a new window is created on the screen.

In Windows, an installable driver is also a DLL. A program can open, enable, query, disable and close the driver based on instructions written in the DLL file.

DLLs may be found in the Windows directory, Windows\System directory or in an program's directory.

If a program is started and one of its DLL files is missing or damaged, you may receive an error message like: "Cannot find xyz.dll". If a program is started with an outdated DLL file or mismatched DLL files, the error message "Call to undefined dynalink" may be displayed. In these situations, the DLL file must be obtained and placed in the proper directory in order for the program to run correctly.

How to Determine the Origin of a DLL File

To determine the version number, company name or other information about a file:

1. Click Start, point to Find, and then click Files or Folders.
2. In the Named box, type the name of the file you want to find, for example "shell32.dll" (without the quotation marks), click Local Hard Drives or the drive letter you want to search in the Look In box, and then click Find Now.
3. Right-click the file in the list of found files, click Properties, and then click the Version tab.

If the file is a Microsoft file, extract a new copy of the file. For information about extracting Windows files, see the following article in the Microsoft Knowledge Base:
If the Company Name referenced on the Version tab is different than Microsoft, contact the manufacturer for assistance.