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.
Buying a pig in a poke does not make most people particularly comfortable, given that drivers for certain peripherals and older system devices still are in short supply. Scanners and multimedia devices such as webcams were sometimes left inoperative after making the x64 switch, because smaller manufacturers and the so-called "no names" often hesitate to port their drivers to Windows XP x64. One reason is limited resources; another is knowing that customers will likely buy a new product with x64 driver support if necessary.
Having mostly solved these launch problems, Windows XP Professional x64 Edition offers support for 64 bit processors. More than 4 GB of system RAM can be addressed, and the widened data width provides substantial performance improvements using applications ported to, or written for, 64 bit Windows.
However, the memory advantage can turn into a disadvantage if you don't have enough of it. As each data chunk is 64 bits long, 32 bit chunks of a 32 bit legacy application can consume double the memory compared to running under a 32 bit OS. From this point of view, it does not make much sense to run Windows XP x64 with only a small amount of memory. If you go for this latest version, we recommend installing at least a gigabyte of RAM.
For this project we took most of our regular benchmarking suite (32 bit applications only) and compared performance when running 32 bit Windows XP versus Windows XP x64 Edition. The Athlon 64 test system was equipped with two 512 MB DIMMs of DDR400 RAM, and we ran all the benchmarks both with the fastest single core processor, the Athlon 64 FX-57, and its dual core counterpart, the Athlon 64 X2 4800+.