- For 64-bit Windows for x86-64 systems, see Windows XP Professional x64 Edition.
It should not be confused with Windows XP Professional x64 Edition, which is designed for x86 processors supporting the x64 extensions.
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 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 NetMeeting 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.
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.
Security updates were discontinued for Windows XP 64-bit Edition in lieu of Windows XP Professional x64 Edition.