Windows XP 64 Bit Edition was 64-bit only and ran on Intel Itanium processors. Windows XP Professional 64 Bit Edition ran on AMD64 architecture and included 32-bit compatibility with x86 Windows, but not 16-bit compatibility with DOS. It provided a preview of the broken drivers that were part of the Vista rollout.

https://en.wikipedia.org/wiki/Windows_XP_editions#64-bit_edi...