The Windows API, informally WinAPI, is Microsoft's core set of application programming interfaces (APIs) available in the Microsoft Windows operating systems. It was formerly called the Win32 API; however, the name Windows API more accurately reflects its roots in 16-bit Windows and its support on 64-bit Windows. Almost all Windows programs interact with the Windows API; a small number (such as programs started early in the Windows startup process) use the Native API [1]. The Microsoft Windows SDK (Software Development Kit) is available for Windows, which provides documentation and tools to enable developers to create software using the Windows API and associated Windows technologies.