Windows XP 64-Bit Edition

Windows XP 64-Bit Edition is an edition of Windows XP designed for Itanium processors. Two versions of this edition were released; one that uses the original Windows XP codebase and another that uses the Windows Server 2003 codebase. Both editions were discontinued in January 2005 after HP, the last distributor of Itanium workstations, ended sales for their Itanium-based workstations in September 2004.

Version 2002
The initial release of Windows XP 64-Bit Edition (oficially marketed as Windows XP 64-Bit Edition for Itanium Systems) was released on 25 October 2001 simultaneously with Windows XP for x86 machines. It was notable for lack of certain features, unlike in the x86 edition, such as Windows Media Player, NetMeeting and support for 16-bit applications.

A compatibility layer called WoW64 allowed the execution of applications compiled for x86 versions of Windows. This compatibility layer used an on-chip decoder integrated into the Itanium processor. However compared to natively compiled software, this decoder was deemed to be extremely slow compared to IA-64 binaries and was later replaced with a faster software translation layer.

Only Service Pack 1 was released for this edition of Windows XP, despite Service Pack 2 for Windows XP x86 being released before the announcement to end support for the IA-64 editions.

Version 2003
The second release of Windows XP 64-Bit Edition which calls itself Version 2003 was released on 28 March 2003. This version adds support for the Itanium 2 processors and is based on the Windows Server 2003 codebase. Unlike x86 versions of Windows XP, it didn't have the Luna theme and was still missing several features compared to the x86 versions of Windows XP.

Since the decision to end support for this version of Windows was made during the development of Service Pack 1, only pre-release builds up to build 3790.1260 can be installed. All later builds can only be installed on Windows Server 2003 and will fail with an error message when attempting to install them on Windows XP 64-Bit Edition, Version 2003. It is however possible to install both RTM versions of Service Pack 1 and Service Pack 2 for Windows Server 2003 with a workaround.