A dll file is a file of code and data that can be used by multiple applications simultaneously. These files are stored in a dll library in the system registry. DLL files contain information necessary to carry out a specific task. Many different programs use the same information to carry out similar tasks. By storing this information in DLL files in the DLL library, programmers are able to use less space to store programs as well as conserve memory usage while running multiple programs at the same time.

Since the DLL file information is not loaded into random access memory with the rest of the program, less memory is required to run a program. Applications can create links to the data in the DLL files either with a dynamic or static link, allowing the application to access the data only when necessary to execute a task.

Often files in dll library can become corrupted or deleted and cause errors in program function. This can be caused in multiple ways. Improperly removing programs from the computer can often cause important DLL files in the DLL library to also become deleted or corrupted. Replacing missing files from the dll library is usually a quick and easy way to fix these errors. Reinstalling any recently removed software is one way to replace missing or corrupt DLL files in the DLL library. When the software is reinstalled, the necessary DLL files are often installed with it. Replacement DLL files for the DLL library are also available for download on several different websites, often at no cost.

Other errors occur when files in the dll library become tagged with the wrong file extensions. Reregistering the file in the dll library with the correct file extension will place the needed file back into the DLL library in its proper place.