Though not yet available in retail channels, Windows XP x64 is a tempting solution for enthusiast users. We discuss its pros and cons and compare how it and conventional Windows XP handle 32 bit applications. Shortly after the release of Windows XP Professional x64 Edition, Microsoft attempted to attract customers to the new version by offering a free Windows exchange program. Owners of Windows XP Professional could upgrade to x64 for free - the catch was that they had to trade-in their 32 bit license permanently.

Toms Hardware Guide