These are collections of pre-written software which provide functionality for other programs. For example hardware drivers are an example of library code. This code is shared between many different applications so they do not have to re-invent the wheel. The OS provides a lot of the library code required for most applications. For example code to talk over a computer network is stored in a library program which can be used by email, browsers and even other library programs. Library programs on windows take the form of DLL (Dynamic link libraries).