WoW64 (Windows 32-bit on Windows 64-bit) is a subsystem of the Windows operating systems capable of running 32-bit applications that is included in all 64-bit versions of Windows. WoW64 aims to take care of many of the differences between 32-bit Windows and 64-bit Windows for running 32-bit application.
The WoW64 subsystem comprises a lightweight compatibility layer that 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 subsystem is implemented using three dynamic link libraries:
Wow64.dll, the core interface to the Windows kernel that translates 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
Wow64cpu.dll, which takes care of switching the processor from 32-bit to 64-bit mode