64 bit better, thats all
for example 64bit xp
This edition was discontinued in early 2005, after Hewlett Packard, the last distributor of Itanium-based workstations, stopped selling Itanium systems marketed as 'workstations'. As of July 2005, Windows XP 64-Bit Edition is no longer supported, and no further security updates were made available.
Windows XP 64-Bit Edition wasn't marketed as the Itanium version of Microsoft's other Windows XP editions but was a separate edition made solely for the Itanium processor and its 64 bit instructions. It is mostly analogous to Windows XP Professional, but numerous older technologies such as DAO, Jet database, NTVDM and Windows on Windows are no longer present so support for MS-DOS and Win16 applications is absent. The original version also lacks 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.
Unlike previous alternate architecture ports of Windows (Windows NT 4.0 for PowerPC, MIPS R4x00, and Alpha) Windows XP 64-Bit Edition can run standard x86 32-bit applications through its WOW64 (Windows-on-Windows 64 bit) emulation layer. While the original Itanium processor contains 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 allows real time translation of x86 32 bit instructions into IA-64 instructions, allowing 32 bit applications to run (albeit significantly more slowly than native code).