Windows XP 64-bit Edition
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Microsoft Windows XP 64-bit Edition is a release of Windows XP designed for 64-bit systems. There are two versions of Windows XP 64-bit Edition available:
- Microsoft Windows XP 64-bit Edition: For use on Intel's IA64 architecture, as implemented by the Intel Itanium product line.
- Microsoft Windows XP 64-bit Edition for 64-bit Extended Systems: For use on the AMD64 architecture, as implemented by the AMD Opteron and Athlon 64 products.
Compatibility with 32-bit Applications
Windows XP 64-bit Edition includes a technology named WOW64. This technology allows for 32-bit applications using the IA32 instruction set to be executed on Windows XP 64-bit Edition. On all Windows XP 64-bit Edition implementations, WOW64 includes:
- Wow64.dll: Provides core emulation services such as data type conversion and an interface to the Windows NT kernel.
- Wow64win.dll: Provides a wrapper for Win32k.sys.
On the AMD64 architecture, hardware support for 32-bit execution is used. However, on the IA64 architecture, WOW64 additionally includes:
- Wow64cpu.dll: Provides for software emulation of the IA-32 instruction set.
The WOW64 subsystem redirects the following services when dealing with 32-bit applications:
- Windows Registry: 32-bit applications see a different version of the registry to ensure compatibility between DLL and COM object registrations in 32 and 64-bit modes. WOW64 further provides a registry reflector that intelligently incorporates safe parts of the 32-bit registry tree with the main (64-bit) registry.
- File System Redirection: The directory "%systemroot%\System32" is used by the 64-bit operating system for DLL files. WOW64 transparently redirects 32-bit requests for this directory to the "%systemroot%\SysWOW64" directory, where 32-bit DLLs are stored.
Windows XP 64-bit Edition does not support the execution of 16-bit Windows or DOS code.
