.dll File — Dynamic Link Library

DLL (Dynamic Link Library) files are shared libraries in the Windows operating system that contain code, data, and resources that can be used by multiple programs simultaneously. DLLs use the same PE (Portable Executable) format as EXE files but are designed to be loaded by other applications rather than executed independently. When multiple programs use the same DLL, only one copy needs to reside in memory, conserving system resources. DLLs export functions through an export table that other applications can call, and import functions from other DLLs through an import table. The Windows API itself is implemented as a collection of DLLs (kernel32.dll, user32.dll, ntdll.dll, etc.). DLLs support versioning, though "DLL Hell" — conflicts between different versions of the same DLL needed by different applications — was a notorious problem addressed by side-by-side assemblies and the .NET Global Assembly Cache. DLLs can be loaded at program startup (load-time linking) or on demand (runtime linking via LoadLibrary). Plugin architectures, device drivers, COM components, and .NET assemblies all use the DLL format. The equivalent formats on other platforms are .so (Linux) and .dylib (macOS).