The %windir%\System32 directory is reserved for 64-bit applications. Most DLL file names were not changed when 64-bit versions of the DLLs were created, so 32-bit versions of the DLLs are stored in a different directory. WOW64 hides this difference by using a file system redirector.
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. Technically, WoW64 is implemented using three dynamic-link libraries (DLLs):
Wow64.dll, the core interface to the Windows NT 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
