Oh, x64, how you tease me. A year ago, I purchased an x64-based PC (a HP Pavilion a640n with an Athlon 64 3400+ processor) so I could test Microsoft's x64-based client and desktop operating systems. These include the x64 Editions of Windows Server 2003 and Windows XP Professional x64 Edition (XP x64), the latter of which I've used and written about extensively. It's been a troubled relationship.

On the SuperSite for Windows, I first tackled the x64 platform--which blends 32-bit x86 compatibility with a 64-bit address space--in my Windows XP Professional x64 Edition Preview in September 2004. Back then, XP x64 Edition had just been recast as a first class Windows citizen that would closely follow the feature-set of the mainstream 32-bit version of Windows XP; originally, it was going to be seriously hobbled, offering just a subset of XP Pro's features.

In February 2005, I published a second lengthy preview of XP x64, focusing on the Release Candidate 2 (RC2) version of the product. XP x64 RC2 was a near-final and feature-complete version of the product and I was surprised by its quality. On the other hand, I was shocked by its compatibility issues with common 32-bit software and hardware. In that preview, I advise readers to dual-boot with XP x64 and not migrate immediately to the new system. The compatibility issues, I felt, would dog potential adopters.

For some reason, I never did provide an actual review of the shipping version of XP x64 on the SuperSite for Windows. However, I did keep writing about the product. Also in February, I wrote an article called "XP Goes to 64 Bits" for PC World, which also examine pre-release versions of the fledgling OS. In that article, I again noted the rampant software compatibility issues as the most serious issue.

"Generally, XP x64 shapes up as a solid addition to the XP product line," I wrote. "But given the problems that many users are likely to encounter when attempting to install applications and drivers on XP X64, we advise caution to owners of 64-bit PCs who are thinking of getting the new OS. As the adage goes, if you need it, you probably already know that you need it. This year, the most likely beneficiaries of the transition are software developers, video professionals, designers, people who use scientific applications, and others who can take advantage of x64's large memory capacity. Even they may not see much of a performance boost, however, since most current 64-bit systems support the same amount of RAM as today's x86 PCs."

In May 2005, I tackled XP x64 again for PC World in an article called "64-Bit Windows? Wait for Longhorn." (These two articles were part of a four-article series that won an award for PC World, incidentally). In this review of the final version of XP x64, I advised readers to "hold off on XP x64 but ... consider 64-bit hardware--especially PCs that can address 8GB or more of RAM--when it comes time to buy your next system. That way, you can adopt XP X64--or more likely a 64-bit Longhorn OS--down the road."

Now, almost six months later, and a year after I got my first x64-based PC, I thought it might be interesting to revisit XP x64. What's changed since Microsoft first shipped XP x64?

Nothing has changed

OK, that's a bit harsh. But by and large, the message on XP x64 hasn't changed a bit. Chances are, you don't want or need it. And if you do get it, you'll be disappointed. I can almost guarantee it. To test this opinion, I decided to wipe out my XP x64 partition and start from scratch, and discover whether the compatibility issues had improved at all.

From a hardware perspective, things have improved slightly. Both ATI and NVIDIA have released stable video drivers for their mainstream video cards, for example, and my PC was up and running with a pretty clean Device Manager in less than an hour. That's the good news. On the bad news side, all kinds of hardware still won't work. Apple's iPods and other MP3 players are a good example. My scanner. And so on.

If you can get over the hardware blues, software incompatibilities will kill you. As I did with the RC2 version of XP x64 in that second preview, I kept detailed records of my two installs of the final version of XP x64 (first in the spring and the again last week). And my experience tell an ugly story.

First, the good news. A surprising number of applications install and run just fine, including Adobe Photoshop Elements 3.01, Adobe Premiere Elements 1.0, Adobe Reader 7.03, Apple iTunes, Apple QuickTime, Google Talk, Microsoft AntiSpyware, Microsoft Digital Image Suite 10 (but not the bundled Photo Story 3.1, which silently did not install), Microsoft Office 2003 SP1, Microsoft FrontPage 2003 SP1, Microsoft OneNote 2003 SP1, Mozilla Firefox 1.0.6, MSN Messenger 7.5, Napster, Nero 6.6, Picasa 2, and Yahoo! Music Engine.

On the hand, a number of applications I use regularly would not install. These include Diskeeper Pro 9, Microsoft Virtual PC 2004, Microsoft Command Here PowerToy, Google Desktop Search 2.0, SecureZIP 8, Microsoft TweakUI PowerToy, and Zone Alarm Suite.

Users concerned about security utilities will be happy to hear that there are finally some mainstream antivirus utilities available for XP x64--I'm currently testing eTrust AntiVirus from Computer Associates, which appears to work well and is reasonably inexpensive. But companies such as McAfee, Symantec, and Zone Alarm still haven't provided x64 versions of their popular antivirus packages and, alas, might not bother.

Games? Not so bad. I installed DOOM 3, Far Cry, Half-Life 2 and Steam, Painkiller and Painkiller Battle Out of Hell, STAR WARS: Battlefront, and Unreal Tournament 2004, and they all ran just fine. Very few games, like Far Cry, are actually available in native x64 versions, but I haven't tested that yet.

What's the point?

It's unclear what purpose XP x64 serves, since most x64-based PCs don't offer more RAM than their 32-bit counterparts anyway. In some ways, XP x64 is almost like a proof of concept. It shows that Microsoft is still capable of targeting multiple platforms and doing so in ways that take advantage of the unique features of each. On x64, Windows XP can theoretically access massive amounts of RAM, but few users will ever take advantage of that. XP x64 is also slightly more secure than 32-bit versions of XP, thanks to its ability to utilize the underlying hardware to implement Data Execution Protection (DEP).

Ultimately, the numerous compatibility issues will prove to be XP x64's Achilles heel and I can't imagine any mainstream user being happy with this OS as a result. My gut feeling is that Microsoft is just biding its time until Windows Vista ships, and at that point the overwhelming number of x64 systems out there will put hardware and software support over the top. Until then, it's a non-starter, save for the most niche possible markets. As I wrote previously about this release, if you need it, you already know you need it. Otherwise, steer clear.

Conclusions

I have mixed feelings about Windows XP Professional x64 Edition. Microsoft did an amazing job of replicating XP Pro on a completely new hardware platform, and so many technology mavens would love to upgrade to this technically excellent system. But the real victims, of course, are those people who foolishly make an attempt at running XP x64. It's just not a viable OS today. But remember this moment, folks. Today, XP x64 is just like Windows for Workgroups 3.11 was in 1994: It had virtually all of the advanced 32-bit technology Microsoft would later tout in Windows 95, though few people noticed at the time. XP x64 will have a similarly uneventful impact on the PC market. But behind the scenes, we're looking at the foundation for the mainstream x64 versions of Windows Vista that will begin shipping next year. By that time, hopefully, the many issues I have with XP x64 will be rendered obsolete.