The runtime library (RTL for short) is literally the library file that a program needs when it's running. It is usually provided in the form of dynamic-link library (DLL for short), and generally includes various functions that are commonly used in programming. It is a practical way to implement the concept of sharing function libraries in Windows. The extensions of these library function files are mainly *.dll, *.ocx (ActiveX control library), and *.drv (old system driver).

In the daily usage of Windows, we occasionally meet system or software errors/prompts like: "***.dll file is missing, xxx can't start...", causing us not to be able to run some software, especially a lot of games. In this case, the first thing we think of is often to search the error message and then download, install and register the corresponding missing DLL files, so as to achieve a manual repair. Therefore, this is not a troublesome thing for just a few missing DLL files, but too many, it will make a user feel hard to accept.