Windows on Windows

In computing, Windows on Windows - commonly referred to as 16-bit WOW, WOWEXEC or simply by its acronym WOW - is a compatibility layer of 32-bit versions of the Microsoft Windows NT family of operating systems that extends the NTVDM to provide limited support for running legacy Win16 applications written for Windows 3.x. With 64-bit-based systems "WOW" generally refers to support for running 32-bit applications on 64-bit versions of Windows, known as WOW64.