A dll is a short for dynamic link library, dll is a windows pe (portable executable) file that application writers use in software for several reasons, as dll files are widely in use in the windows operation system most of today software has between one to more dll files for the software to use, a dll file contain external function that the software can use the big advantage of using a dll file is in case of changes, instead of changing all the application the developer can change the function that need to be change and by that only replacing the dll can be the solution to the problem.

Reasons to use dll files:

  1. a dll file can be use in more then one application, like the file->save menu that windows operation system use in a lot of places.
  2. in case of a problem or error you can fix it in the dll and only update it.
  3. in case of new features you can add them to the dll and update it, this way older version that will use the new dll continue to work and new version will have the new features.

what is a dll?
Dynamic link library, or dll, is a normal pe file that the big difference from it to a normal pe file,re exe, is a small change in one bit in the structure of the file, a pe file contain a header and an external header and so on, so the big diff is a change in the header, this is from the inner structure of the dll, as you cant run it like a normal exe file you can load it in run time if it needed in your software.

There are a lot of api call that you use when developing application for the Windows operation system and a lot of the api (application programming interface) call are store in system dll files.

When there are missing dll files in the system you will get an error message that can indicate the missing required dll file name, and if your system is not crashing due to the missing dll files you can download the missing dll files from the internet or from the original installation disk and add them to the system to the right directory and from then the application will work.

Most of the service pack and software updates that the operation system and other installed software are doing are downloading new dll files that replace the old ones, some of them contains bug fix and new features to the installed application.