Windows XP Professional x64 Edition

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.

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

• Microsoft.com – Windows XP Professional 64-bit Edition Home Page
• PlanetAMD64.com – Forums, 64bit Software Database, 64bit Driver Database, 64bit News

Drivers

• ATi.com – ATI Display 64bit Driver
• Nvidia.com – Nvidia Display 64bit Driver