Cast your mind back to September 03 and you might remember AMD's shock announcement that it thought we were all ready for 64bit computing. AMD put its money where its mouth was and released the Athlon 64 - a great product but one that was a lone outsider in a 32bit world, with not so much as a sniff of good Samaritan support from software and hardware developers. In retrospect, however, AMD's move looks inspired.

At the time Intel and Microsoft publicly proclaimed a lack of interest, suggesting that us commoners would be indifferent to the benefits of 64bit technology. But as it turns out both companies were privately beavering away on releases.

Now Microsoft has announced its first 64bit operating system for mainstream desktops - Windows XP Professional X64 Edition - will arrive by the middle of this year. In anticipation of the event, it has delivered its initial Release Candidate (RC1) of the operating system.

This is not the first 64bit OS the company has produced, but XP X64 is the first Windows system designed to run 32bit apps. Only with a 64bit OS and applications can early adopters enjoy everything 64bit computing has to offer, including access to up to 16TB (terabytes) of RAM.

Lasting memory

While RC1 supports only 32GB of RAM, Microsoft says that the final OS will support 128GB – as well as 16TB of virtual memory. Still, that's way beyond the 4GB maximum of today's 32bit systems.

In real terms, it translates into greater speeds: 64bit apps won't have to swap large data sets between memory and disk, therefore loading the data more efficiently than 32bit programs can.

Commercial 64bit native applications are not yet available, so we put RC1 through its paces with several popular current 32bit apps - and in general we were impressed. Owners of 64bit PCs can download RC1 from

While an early beta we viewed looked more like Windows 2000, XP X64 was originally conceived as a stripped-down version of the Windows XP operating system. It was recast early last year after Microsoft finally concluded that X64-based PCs were likely to become mainstream by the end of 2005.

Consequently, RC1 is a vast improvement over previous beta releases, offering most of the functionality of today's 32bit Windows XP Pro with Service Pack 2 (SP2), including the Security Center and pop-up blocking in Internet Explorer. Windows XP X64 RC1 also includes the 32bit version of Windows Media Player 10.0.

Only a few technologies from today's XP are absent from X64. These include the 16bit subsystem that enables DOS and 16bit Windows applications to run. Because many 32bit applications continue to use 16bit installers, however, that means they can't be loaded up on an XP X64 system. Microsoft says that it's working with application makers to get 32bit installers completed.

That familiar feeling

In use, XP X64 feels quite similar to 32bit versions of Windows - with a few noteworthy exceptions. The Start menu, for example, has two versions of Internet Explorer: a new 64bit release and the same 32bit version that Microsoft shipped in XP SP2.

Why? Since 32bit plug-ins for IE won't run in the 64bit version, Microsoft had to retain the 32bit version for people who want to keep using legacy IE add-ons, such as QuickTime or Google Toolbar.

From a performance perspective, XP X64 appears to work as well as 32bit Windows XP Professional on the same hardware. With the OS and beta 64bit drivers loaded on an Athlon 64-based Micro Express PC, nine of the 13 tests in our WorldBench 5 benchmark suite ran without a hitch. Not bad going. The other four only failed on minor issues, mostly relating to licence key validation.

Results were generally close to those achieved by the same desktop running XP Pro. In some instances XP Pro was a bit faster, while in others XP X64 was ahead.

However, a number of applications wouldn't install, including several Microsoft ones. Some of these had been written for specific versions of Windows, such as PowerToys for Windows XP and most major antivirus and security packages. We also couldn't install the beta of MSN Toolbar Suite and the finished version of Photo Story 3.0. Office 2003 SP1 did install, but only after displaying a confusing error message.

In the works

Only when it's possible to get hold of applications that can capitalise on its huge memory resources will 64bit computing have any impact on the average PC desktop. Several companies have made vague promises about developing native 64bit programs, but none has unveiled any detailed plans as yet.

NewTek says it will port its award-winning LightWave 3D graphics and visual effects package to X64 sometime this year. Epic Games has also pledged to release a 64bit version of its Unreal Tournament 2004, but this has yet to materialise. Still, the crucial factor is mainstream application support from Microsoft, Adobe, and other big names.

Hardware device drivers are another problem. Today's 32bit drivers won't install on XP X64; and even though RC1 includes a wide range of drivers for popular devices, the absence of third-party drivers will torment many users.

We managed to find beta 64bit drivers for nVidia graphics cards and Creative Labs sound cards. But 64bit drivers for other hardware, such as HP scanners, just don't exist.

Generally, XP X64 shapes up as a solid addition to the XP product line. 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 64bit PCs who are thinking of getting the new OS.

At this stage in its development, people who can exploit its large memory resources such as software developers, video professionals, designers and those who use scientific applications are the most likely to benefit from this OS. But even they may not see much of a performance boost, since most current 64bit systems only have the same amount of RAM as today's x86 PCs.

Microsoft also plans to provide a Technology Exchange Program to allow customers who bought 64bit PCs with Windows XP Pro to swap it for XP X64. The details are yet to be finalised, but the company intends to supply Product Keys with the new OS and then deactivate the 32bit Product Keys.

You can't simply upgrade an XP Pro PC to XP X64, however. You can acquire XP X64 only as a clean install, which entails backing up your existing data, installing the OS from scratch, and then reinstalling your apps.

Microsoft Windows XP Professional X64 Edition: Specs

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We can't really give you the full lowdown on XP X64 until it's supported across the board by software and hardware makers. But as far as this pre-release version goes, we can tell you things are looking good for Microsoft's next big product. To the relief of many, XP X64 appears to work as well for consumers using 32bit environments, but it's still only an option for the more adventurous. For everyone else, it is better to hang on until 64bit computing works seamlessly.