Recently I've been hearing from a lot of users who have expressed interest in 64-bit Windows XP. They usually have a lot of questions about performance and application availability and wonder whether they'll have to upgrade their hardware if they plan to use the new 64-bit OS.
I answer as many questions as I can, but I can't answer them all because I don't know how the users who are asking about using 64-bit Windows are using their computers. How you plan to use the new OS is crucial in determining whether the OS is suitable for you. Microsoft realizes this, and has made a trial version of the OS available.
You can download XP Professional x64 Edition software at http://www.microsoft.com/windowsxp/64bit/evaluation/trial.mspx . This Web site will let you order the OS on CD-ROM (for free in the United States) or, if you have a fast enough connection, you can download a 550MB ISO image and burn your own installation CD-ROM. After you create an installation CD-ROM, you can copy the files to a network share in the same manner you would with other versions of Windows.
I don't suggest that you install the new OS on a production system (and you can't upgrade 32-bit Windows to 64-bit Windows, anyway) because the best way to get rid of the trial version is going to be to reformat and reinstall the OS of choice. The 64-bit OS will install on any AMD 64-bit processor as well as any Intel Extended Memory 64 Technology (EM64T) processor, and although the site states that it requires only 256MB of RAM to use the 64-bit OS, you'll want at least 1GB. However, to really test the advantages of a 64-bit system, you'll want to try it out with at least 4GB of RAM or even more if you have a motherboard that will support larger amounts of memory.
Although 64-bit programs are available, desktop users will most likely be running 32-bit applications. This means you'll be using the Windows on Windows64 (WOW64) subsystem, which allows 32-bit programs to run, unmodified, on 64-bit Windows. It does this by creating a 32-bit virtual environment in which those programs can run. Most 32-bit programs will run more slowly under WOW64 than they would run natively under 32-bit Windows, but if you have programs that can benefit from large amounts of available memory, they might see a performance improvement under 64-bit Windows.
You'll likely find that even if your applications do well under 64-bit Windows, the tools and utilities that you use on a daily basis in 32-bit Windows might not be available at all under the 64-bit version. Applications that access the core components of the OS will need to have native 64-bit versions available, meaning that after everything is said and done, 64-bit Windows will remain a special purpose OS for the near future.