Windows XP Professional x64 Edition

From Academic Kids

Windows XP Professional 64-bit Edition released on April 25 2005 by Microsoft is a variation of the typical 32-bit Windows XP operating system. It is designed to use 64-bit memory addresses which increases the maximum allowable system memory (RAM) past the 32-bit limit of 4 GB, though it is currently limited to 128 GB (237) of physical RAM and 16 TB (244) of virtual RAM. It is currently only available for sale as an OEM product.


Compatibility with 32-bit applications

Windows XP 64-bit Edition uses a technology named WOW64, to allow it to run 32-bit applications using the IA32 instruction set. This consists of:

  • Wow64.dll - provides the core emulation services such as data type conversion and an interface to the Windows NT kernel
  • Wow64win.dll - provides a wrapper for the majority of the Win32 API
  • Wow64cpu.dll - provides for switching the processor between 32-bit and 64-bit modes

Since the AMD64 architecture includes hardware support for 32-bit execution, WOW64 can just simply switch the process between 32-bit and 64-bit modes. However, on the IA64 architecture, WOW64 has to translate 32-bit instructions into 64-bit that the processor can execute. This means the AMD64 based processors are much more efficient at running 32-bit applications than IA64 based processors.

Although 32-bit applications can be transparently run, the mixing of the two types of code within the same process is not possible. A 64-bit application cannot load a 32-bit DLL into its process space, and similarly a 32-bit application cannot load a 64-bit DLL into its process space. This may lead to the need for DLL and COM developers to provide their libraries in both 32-bit and 64-bit editions, in order to accomodate being loaded by an application of either bitness. Windows XP 64-bit Edition includes both a 32-bit and a 64-bit edition of Internet Explorer in order to allow for the possibility that some third-party browser plugins or ActiveX controls may not yet be available in a 64-bit version. 32-bit drivers are not supported by Windows XP 64-bit Edition, so the users will have to wait until all their hardware is supported by the hardware vendor with 64-bit drivers [1] (

The WOW64 subsystem also 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.

Compatibility with 16-bit applications

Unlike other versions of Windows XP, Windows XP Professional 64-bit Edition does not support the execution of 16-bit Windows or DOS code.

External links


zh:Windows XP Professional x64 Edition


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