What is a DLL File?

Basic definition of a DLL file:

DLL is the abbreviation for Dynamic Link Library. A DLL is an executable file that contains some functionality at runtime and it will be shared by many applications. DLL files are not invoked manually by a user, but are called by either a DLL file or an executable file. Microsoft Windows provides a lot of DLL files, that are used by applications to run in Windws.

Example of DLL files:

msi.dll: msi.dll is component that contains functions used to install MSI (Microsoft Installer) packages.

name.dll: The NameCtrl Control, defined in the Microsoft name.dll file, is an ActiveX control that allows a web page to display presence information for people allowing the user to take various actions with respect to those people through an on-object user interface in Windows SharePoint Services. This DLL is installed on the client computer during the Microsoft Office 2007 system setup.

Why should we use DLLs?

Many programs have a huge number of functions that are only used occasionally. Breaking up an application into separate DLLs saves memory by keeping routines / functions on the hard disk until required. Application DLLs can also be made sharable so that other applications will use the same DLL.