WoW64

In computing on Microsoft platforms, WoW64 (Windows 32-bit on Windows 64-bit) is a subsystem of the Windows operating system capable of running 32-bit applications on 64-bit Windows. It is included in all 64-bit versions of Windows, except in Windows Server Server Core where it is an optional component, and Windows Nano Server where it is not included. WoW64 aims to take care of many of the differences between 32-bit Windows and 64-bit Windows, particularly involving structural changes to Windows itself.

==Translation libraries== The WoW64 subsystem comprises a lightweight compatibility layer that has similar interfaces on all 64-bit versions of Windows. It aims to create a 32-bit environment that provides the interfaces required to run unmodified 32-bit Windows applications on a 64-bit system. WOW64 is implemented using several DLLs, some of which include: Wow64.dll, the core interface to the Windows NT kernel that translates (thunks) between 32-bit and 64-bit calls, including pointer and call stack manipulations Wow64win.dll, which provides the appropriate entry-points for 32-bit applications (win32k thunks) A dll that allows 32-bit x86 instructions to be executed, which varies by instruction set architecture. On x86-64, Wow64cpu.dll takes care of switching the processor from 32-bit to 64-bit mode. This is computationally cheap, as x86-64 machines have a native mode for running 32-bit x86 code. On IA-64 (Itanium 2), three files are needed for a slower software emulation: Wow64cpu.dll, a "CPU abstraction layer"; , the x86 software emulator; and , the bridge between the emulator and the WOW64 system. On ARMv8 64-bit, for x86 emulation, and for switching to ARM32 mode.