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Reference.org
Dynamic-link library
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<p>A dynamic-link library (DLL) is a <a href="/facts/Shared_library/xRzL3P7q">shared library</a> in the <a href="/facts/Microsoft/nGIDDXdx">Microsoft</a> <a href="/facts/Microsoft_Windows/bwhAhuSL">Windows</a> or <a href="/facts/OS/2/uVBl6ItP">OS/2</a> <a href="/facts/Operating_system/8XTuvMh2">operating system</a>. A DLL can contain <a href="/facts/Executable_code/VSst9eLA">executable code</a> (functions), <a href="/facts/Data_(computing)/cPjfFHph">data</a>, and <a href="/facts/Resource_(Windows)/n8sNHBol">resources</a>. </p><p>A DLL file often has <a href="/facts/File_extension/cJgfAym4">file extension</a> .dll even though this is not required. The extension is sometimes used to describe the content of the file. For example, .ocx is a common extension for an <a href="/facts/ActiveX/xJb7t7Eh">ActiveX</a> control and .drv for a legacy (16-bit) <a href="/facts/Device_driver/rDYnHU1G">device driver</a>. </p><p>A DLL that contains only resources can be called a <i>resource DLL</i>. Examples include an <a href="/facts/Icon_(computing)/habCR8KJ">icon</a> library, with common extension .icl, and a <a href="/facts/Typeface/It41hIjl">font</a> library with common extensions .fon and .fot. </p><p>The <a href="/facts/File_format/qrXbwJaH">file format</a> of a DLL is the same as for an <a href="/facts/Executable/VSst9eLA">executable</a> (a.k.a. <a href="/facts/EXE/xgRXf4rt">EXE</a>). The main difference between a DLL file and an EXE file is that a DLL cannot be run directly since the operating system requires an <a href="/facts/Entry_point/nN52vHKb">entry point</a> to start execution. Windows provides a utility program (RUNDLL.EXE/RUNDLL32.EXE) to execute a function exposed by a DLL. Since they have the same format, an EXE can be used as a DLL. Consuming code can load an EXE via the same mechanism as loading a DLL. </p>