Windows XP Professional x64 Edition

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For 64-bit Windows for Itanium systems, see Windows XP 64-bit Edition.

Template:Infobox OS Microsoft Windows XP Professional x64 Edition released on April 25, 2005 by Microsoft is a variation of the typical 32-bit Windows XP operating system for x86 personal computers.

Windows XP Professional x64 Edition is based upon Windows Server 2003 SP1 (build 5.2.3790.1830) as that was the latest version of Microsoft Windows during the operating system's development, but takes Windows XP as its name. It is designed to use the expanded 64-bit memory address space provided by the AMD64 architecture (referred to as EM64T by Intel in their implementation) and other future x86-based 64-bit (x86-64) processors.

The primary benefit of moving to 64-bit is the increase in the maximum allocatable system memory (RAM). Windows XP 32-bit is limited to a total of 4 GB, which is equally divided between Kernel and application usage. Windows XP x64 can support much more memory; although the theoretical memory limit a 64-bit computer can address is about 18 billion GB (18 exabytes), Windows XP x64 is currently limited to 128 GB (<math>2^{37}</math> bytes) of physical memory and 16 TB (<math>2^{44}</math> bytes) of virtual memory. Microsoft claims this limit will be increased as hardware capabilities improve. In practice, most motherboards compatible with 64-bit processors do not support nearly the maximum, and often retain the 4 GB limit.

This Windows XP x64 Edition is not to be confused with Windows XP 64-bit Edition, as the latter was designed for IA-64 Intel Itanium processors. [1][2], although they both are commonly referred to as '64-bit Windows' by Microsoft due to their similarities from developer's point of view.

1 Compatibility with 32-bit applications
2 Compatibility with 16-bit applications
3 Windows 64-bit applications
4 Trivia
5 External links
- 5.1 Drivers

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Compatibility with 32-bit applications

Windows XP x64 Edition uses a technology named WOW64, which permits the execution of 32-bit x86 applications. It was first employed in Windows XP 64-bit Edition but then reused for x64 editions of Windows XP and Windows Server 2003.

Since the AMD64 architecture includes hardware-level support for 32-bit instructions, WOW64 simply switches the process between 32- and 64-bit modes. However, on the IA64/Itanium architecture, WOW64 has to translate 32-bit instructions into their 64-bit equivalents such that the processor can execute them. As a result, AMD64 microprocessors suffer small or even unnoticeable performance loss when executing 32-bit Windows applications, whereas IA64 implementations experience noticeable performance loss.

Although 32-bit applications can be run transparently, the mixing of the two types of code within the same process is not allowed. A 64-bit application cannot link against a 32-bit library (DLL) and similarly a 32-bit application cannot link against a 64-bit library. This may lead to the need for library developers to provide both 32- and 64-bit versions of their files. Windows XP x64 Edition includes both 32- and 64-bit versions 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 64-bit versions.

Older 32-bit drivers and services are not supported by 64-bit Windows, but video and audio codecs such as XviD or OggDS, which are in fact 32-bit DLLs are supported as long as the media player that uses them is 32-bit as well. This includes popular video players such as Media Player Classic.

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Compatibility with 16-bit applications

Unlike prior versions of the Windows NT line, 64-bit Windows versions do not include NTVDM so there is no support for the execution of MS-DOS, POSIX, OS/2 1.x and 16-bit Windows applications, although there are 3rd-party software emulators such as DOSBox that can be used to run DOS programs.

Another solution is to use virtualization software like VMware and VirtualPC to run copies of MS-DOS and Windows 3.1.

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Windows 64-bit applications

See Microsoft Windows 64-bit applications

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Trivia

During the initial development phases (2003-2004), Windows XP x64 was named Windows XP 64-bit Edition for x86 Extended systems and later, Windows XP 64-bit Edition for Extended systems, as opposed to '64-bit Edition for Itanium systems'.

The source code for Windows XP x64 is based on Windows Server 2003, and not the 32-bit version of Windows XP as one might expect. This is evidenced by the fact that both Windows XP x64 and Windows 2003 share the same version and build numbers (5.2.3790). This also means that Windows XP x64 is the only version of XP to ship with IIS 6.0 (all other versions of XP have 5.1).

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