Windows XP 64-bit Edition


 * For Windows XP for x86-64 systems, see Windows XP Professional x64 Edition.

Microsoft Windows XP 64-bit Edition was a version of Microsoft's Windows XP operating system designed to run on Intel's Itanium family of processors, in their native 64-bit mode.

It should not be confused with Windows XP Professional x64 Edition, which is designed for x86 processors supporting the x64 extensions.

Releases
Two major versions of Windows 64-bit Edition were released:
 * Windows XP 64-bit Edition for Itanium systems, Version 2002 — Based on Windows XP codebase, which was released in 2001
 * Windows XP 64-bit Edition, Version 2003 — Based on Windows Server 2003 codebase, which added support for the Itanium 2 processor, was released to manufacturing on March 28, 2003.

It should be noted that Windows XP 64-bit didn't fall into one of Microsoft's then current Windows XP product lines (Home, Professional, Media Center or Tablet) but was a separate edition made solely for the Itanium processor and its 64-bit instructions. However it was mostly analogous to Windows XP Professional Edition, but with some limitations:


 * Initially it lacked most media applications such as Windows Media Player, NetMeeting, Windows Movie Maker, and integrated CD burning, although WMP and Net Meeting were added in the 2003 version.
 * Numerous old technologies such as DAO, Jet database and most notably NTVDM were removed, so support for MS-DOS, POSIX, OS/2, and Win16 applications is absent.

32-bit support
However, unlike previous alternate architecture ports of Windows (Windows NT 4.0 for PowerPC, MIPS R4x00, and Alpha) Windows XP 64-bit Edition could run standard x86 32-bit applications through its WOW64 (Windows on Windows) emulation layer. While the original Itanium processor contained an on-chip IA-32 decoder, it was deemed far too slow for serious use (running at about 400 MHz), so Microsoft and Intel wrote a software 32 to 64 bit translator dubbed the IA-32 Execution Layer. It allowed real time translation of x86 32-bit instructions into IA-64 instructions, allowing legacy 32-bit applications to run (albeit significantly more slowly than native code).

However, Windows XP 64-bit Edition could not use 32-bit drivers and services except for codecs such as XviD, which were actually 32-bit DLLs so they could be used if media players are 32-bit. Thus, many older devices are incompatible with this version of Windows.

Discontinuation
Support for Windows XP 64-bit Edition ended on June 30, 2005. Security updates were discontinued in favor of Windows XP Professional x64 Edition.