Dynamic Link Library

What Does Dynamic Link Library Mean?

A dynamic link library (DLL) is a shared program module with ordered code, methods, functions, enums and structures that may be dynamically called by an executing program during run time. A DLL usually has a file extension ending in .dll. Other file extensions are .drv and .ocx.

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DLLs were developed by Microsoft and work only with the Windows operating system (OS).

Techopedia Explains Dynamic Link Library

DLL-defined function types are as follows:

  • Exported: May be called by another module, as well as from their defined DLLs
  • Internal: May only be called from their defined DLLs

DLLs help conserve system memory. They are not loaded into RAM until they are needed, and thus help reduce memory overhead. Applications that require DLL data receive it as required, which also helps manage memory.

Links to required DLL files are usually created during programming. If the links are static, DLL files are available and used as the program runs. If the links are dynamic, DLL files are used only as needed.

Another advantage of DLL files is that they may be used by multiple programs simultaneously. DLL files are usually not opened directly because they are automatically loaded with the program. DLL files also use system resources efficiently and reduce swapping.

When DLL functions change, it is not necessary to recompile or relink the application using the DLL as long as the calling conventions, function arguments and return values remain the same.

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Margaret Rouse
Technology Expert

Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.