'''Windows on Windows''', commonly referred to as '''WOW''' or '''WoW''', is ana name of two abstraction subsystemsubsystems of [[Microsoft]] [[Microsoft Windows|Windows]] [[operating system]]. WowWoW is a name of two critical componentcomponents for [[backwards compatibility]] of [[legacy code]] as Windows progresses. The first Wowcomponent called WoW appeared in [[Windows NT]] to support applications using the [[Win16]] [[API]] and was relying on [[NTVDM]].
Supporting [[Win32]] applications on [[Windows XP Professional x64 Edition]], [[Windows Server 2003]] x64 and other x64 versions of Windows requires a new WowWoW called [[WOW64|WoW64]]. The x64 versions of Windows no longer include the 16 bit WoW subsystem (as well as the NTVDM) and can therefore no longer run 16-bit Windows nor DOS applications.
