WOW is an acronym for Windows On Windows, or more precisely Windows 3.1 on Windows 2K (NT). WOW is a program designed by Microsoft, which allows 16-bit programs to operate under their 32-bit operating systems. The WOW subsystem is closely related to the Virtual DOS Machine (VDM) that NT uses to execute 16-bit DOS applications. WOW is a user mode program entitled WOWEXEC.EXE. By default, WOW is executed automatically, by Windows, when a user starts to operate a 16-bit program, such as DFW. Initially, the use of WOW is transparent to the user and the uninitiated PC user will be unaware of its presence.