Windows on Windows (WoW64)

Code execution is enable in both the above kind of platforms in two ways

·         Native 64-bit

·         WoW64 x86 emulator

While as the name implies, native 64-bit takes advantage of the native 64-bit computing platform, Windows-On-Windows environment, WoW, WOW64 etc. are all names that refer to an x86 emulator that allows 32-bit Windows-based applications to run on 64-bit Windows. Wow64 allows 32-bit productivity applications developed using the .NET Framework 1.0, 1.1 and 2.0 and Win32 to run on 64-bit Windows and take advantage of the 64-bit Windows kernel which offers a larger number of kernel handles and window handles. WoW64 supports 32-bit console, GUI and service application, and although some 32-bit server applications may be certified to run on WoW64, WoW64 is NOT intended for 32-bit server apps. WoW64 does NOT support 16-bit Windows apps.

WoW64 emulation is performed natively (on the chip) by the x64 micro-architecture, which means WoW64 performance on x64 is similar to that of 32-bit Windows. However, because the Itanium (IA64) architecture does not support native WoW64 emulation, WoW64 performance on the Itanium is substantially less than that of 32-bit Windows.

From MSDN blog:  blogs.msdn.com/b/gauravseth/archive/2006/04/24/582091.aspx

From MSDN Dev Center:  https://msdn.microsoft.com/en-us/library/windows/desktop/aa384274%28v=vs.85%29.aspx