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Microsoft Windows XP 64-bit Edition was a version of Microsoft's Windows XP operating system designed to run on Intel Itanium family of microprocessors 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. Two major versions of Windows 64-bit Edition were released: 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: 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 400MHz), 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 because of the more recent release Windows XP Professional x64 Edition.
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