Windows Vista Feature Focus: 64-Bit (x64) Support

With Windows XP, Microsoft created specific Windows product editions, or SKUs, that targeted 64-bit processors from Intel and AMD. The latest, Windows XP Professional x64 Edition (see my preview and mini-review), is the most interesting of these products because it provides functional parity with the mainstream 32-bit version of XP Professional (with a few key but understandable exceptions including 16-bit support). XP x64 is a surprisingly stable and well-designed product, but it was doomed to failure because of hardware and software incompatibilities: Unlike with 32-bit XP versions, many hardware devices will not work on XP x64 because of a dearth of 64-bit drivers (32-bit drivers will not work in a native 64-bit OS). Likewise, many software applications will not install or run because of various issues, including a surprising amount of 16-bit application installers and poorly-designed version detection.

The x64 versions of Windows Vista adopt all of the positive and negative quirks of their XP x64 predecessor and add a few wrinkles of their own. Like XP x64, the various Vista x64 versions support x64-compatible PCs based on the AMD-64 (Athlon-64, Opteron, Turion processors) and Intel EMT-64 (Pentium D, Xeon, Core Duo, and Core 2 Duo) platforms.

Tip: Windows Vista Ultimate comes with both 32-bit (x86) and 64-bit (x64) versions in the box, on separate DVDs; purhcasers of other retail 32-bit Vista versions can order the 64-bit version from Microsoft for a nominal fee.

For the most part, the x64 support in each Vista edition is identical. One exception is that they each support different amounts of RAM. Vista Home Basic (and Home Basic N) support up to 8 GB of RAM, compared to 4 GB for all 32-bit versions of Vista. Home Premium, meanwhile, supports 16 GB. And Business (and Business N), Enterprise, and Ultimate all support 128 GB or more of memory. (The "or more" bit refers to the fact that there are currently no PCs available yet that suport over 128 GB of RAM; when that happens, these Vista versions will support it.)

Security features

One of the primary benefits of using an x64-based version of Windows Vista is that these versions provide dramatically improved security functionality when compared to their 32-bit counterparts. Most dramatically, the Windows Vista x64 versions include a new secret security feature called Address Space Layout Randmonizer (ASLR) that helps eliminate remote system attacks for the first time on the Windows platform. This feature (which was first disclosed in this very article) ensures that system files load at random (1 in 256) memory offsets at every system boot, compared to previous Windows versions where system files always loaded to the same offset memory location. Because of this change, most (approximately 99 percent) remote attacks will simply fail on x64-based Vista versions.

Working in tandem with the No Execute (NX) technologies in modern x64 microprocessors from both AMD and Intel, Windows Vista x64 versions, like XP x64, also provide support for hardware-backed Data Execution Protection (DEP), which helps to prevent the buffer overflows that are commonly used in electronic attacks. (32-bit Vista versions utilize a less effective, software-based version of DEP.) Another unique x64 feature, Kernel Patch Protection (sometimes called PatchGuard), prevents malicious software from patching the Windows Vista kernel. PatchGuard, Microsoft says, works by preventing kernel-mode drivers from extending or replacing other kernel services and preventing third-party software from patching any part of the kernel.

Tip: Before Windows Vista was finalized, Kernel Patch Protection came under fire from security software vendors who complained that this feature prevented them from patching the Vista kernel and thus protecting users from kernel-based attacked. After some deliberation, Microsoft agreed to let these companies patch the Vista kernel. However, the code needed to do so will not be made available until Windows Vista Service Pack 1 (SP1), due in late 2007.

Additionally, Windows Vista x64 versions require that all drivers be digitally signed by the developer. If you've ever installed a driver in Windows XP, you'll likely be familiar with the unsigned driver dialog, which offers a "Continue Anyway" option when a setup application attempts to load an unsigned driver. In the x64 versions of Windows Vista, this will not be possible. Microsoft says that it is requiring signed drivers so that it can ensure that drivers are of the highest possible quality; poorly-written drivers are, today, still the leading causes of blue screens and other system instability issues.

When taken together, these features ensure that the x64 versions of Windows Vista will be both the most secure and reliable versions of Windows ever created. Likewise, they will be more secure and reliable than the 32-bit Vista versions.

Other unique x64 features

The x64 Vista versions include a few esoteric and unique features that will likely be of interest only to the corporate market. For example, a service called Subsystem for UNIX-based Applications (SUA, previously called Windows Services for UNIX) is included with Vista Enterprise and Ultimate and provides a native 64-bit POSIX (Portable Operating System Interface) subsystem on x64 versions of Windows Vista, the first time such technology has been made available by Microsoft.

Fun fact: Microsoft originally intended to provide another compatibility feature called Virtual PC Express in the x64 versions of Windows Vista Enteprise and Ultimate. However, this feature was removed when the company decided instead to make Virtual PC free to all Windows users.

Compatibility issues and other limitations

Sadly, the various benefits of the x64 Vista versions are counterbalanced by a number of limitations, the most important of which are compatibility issues. 16-bit applications are not supported, which is less problematic than it was a few years ago, but still an issue for some applications that use legacy application installers. 32-bit device drivers are not supported, so you can't use any of the existing hardware drivers out there, but must instead use the subset of x64-based drivers that are currently available. This situation will improve over time, but x64 Vista users are going to be orphaning hardware.

New 64-bit applications will need to adhere to the new Windows Vista application standards in order to run correctly on these versions. That means that even some software written specifically for XP x64 might not work correctly.

Those hoping to upgrade should be aware of a few other issues, too. 32-bit versions of XP can only be upgraded to 32-bit versions of Windows Vista. And Windows XP Professional x64 Edition can only be upgraded to 64-bit versions of Windows Vista (Business and above).

Finally, it's worth noting that while Microsoft is proudly trumpeting the fact that Vista's new modular architecture will allow corporations to rollout Vista to multiple desktop types using only a single Windows Imaging Format (WIM)-based installation image, the truth is a bit more complicated. Companies that plan to rollout both 32-bit and 64-bit Vista versions will need to maintain separate install images for both 32-bit and x64 Vista versions.

Final thoughts

As with Windows XP Professional x64 Edition, the various Windows Vista x64 versions represent a compromise of sorts and are, thus, not necessarily a good choice for most Windows users ... Yet. On the positive side, the x64 versions of Windows Vista are more secure and reliable than the 32-bit versions. The also support enormous amounts of system memory, which can be important in markets such as digital content creation, engineering, and even gaming. On the other hand, the x64 versions are also far less compatible than their predecessors, with both hardware devices and software, and these incompatibilities will ultimately make the x64 Vista versions less attractive to most users. Within the next few years, most Windows users will almost certainly move to x64-based PCs. But I'm guessing that the 32-bit versions of Vista will dominate throughout this product's lifetime because of compatibility issues. Think of Vista as the "line in the sand" for the x64 platform on the client: Post-Vista, it's likely that most compatibility issues will be resolved or rendered moot by new hardware and software versions that are more x64-savvy. By that time, migrating to x64 will be a no-brainer, and hopefully Microsoft will support upgrading 32-bit Vista versions to future 64-bit Windows versions.

--Paul Thurrott
May 25, 2006
Updated February 4, 2007; February 22, 2007