A Dynamic link Library (DLL) is a standardized file format used to store algorithms. Because it is standardized, most Windows development environments can access the routines. A long, long time ago, when there was an operating system called DOS, 'static' link libraries existed. Static link libraries were bound to the final executable at link time. DLL's in contrast, remain as separate modules, allowing for the usage of the same file by multiple executables. This was critical during the initial Windows days, as hard disk space was minuscule by today's standards. DLL's typically have a file extension of *.DLL or *.OCX.