What Do DLL Files Do?
A DLL file is indicated by the extension DLL in its name. Microsoft gives several definitions of a DLL but the one that I think has the least jargon is this: “A Dynamic Link Library (DLL) is a file of code containing functions that can be called from other executable code (either an application or another DLL). Programmers use DLLs to provide code that they can reuse and to parcel out distinct jobs. Unlike an executable (EXE) file, a DLL cannot be directly run. DLLs must be called from other code that is already executing.” Another way of putting it is that DLL files are like modules that can be plugged into different programs whenever a program needs the particular features that come with the DLL. The original concept behind DLL files was to simplify things. It was recognized that there were many functions common to a lot of software. For example, most programs need to create the graphical interface that appears on the screen. Instead of having to contain the code to create the interf