What is a class library / DLL A class library can be seen as a container for code that can be used in different applications. The DLL files saves a lot of space on your hard drive because different application cn use the same code instead of having its own set of duplicated code.
DLL means 'dynamic link library' A DLL consist of a compiled set of classes. The code is often designed to be re-used by other programs and result in less duplicated code. A DLL can be dynamically loaded during run-time - With this kind of modulization we can load the code when we need it, instead of everything at once.
If programs run simultaniously and use the same code it will save both loading time, disk space and memory.
When things are in modulized it means that we can load modules dynamically in run time. That means we don't have to load everything from the start and your large programs can open quickly It is also an great advantage for the developers because modules can be compiled individually so that large program don't have to be recompiled completely every time a developer makes a small change in the code.
If a program needs a certain DLL-files and it isn't available your program will run intp problems. I guess most windows user has experienced at least once that some programs complains about some missing dll-files
When using dll fiels your program becomes depenedent on these libraries and you need to make sure the computer has a recent verion of that dll
When you write DLL-filesUsualyy dll-files are writen in Visual Studio when When you develop a class library