Yes, you read that headline correctly. As this magazine went to press, a variety of notebook PC vendors, including Acer, Fujitsu, and HP, were shipping 64-bit notebook computers running Windows XP. At least some of those notebooks are being tested with Windows XP Professional x64 Edition Release Candidate 2 Customer Preview. The era of 64-bit computing, expected to initially target servers and high-end workstations, seems to be affecting notebook PCs as well. Why? According to Microsoft Senior Product Manager Brian Marr, the phenomenon is being driven by customer demand—specifically, from enthusiast end users.

Marr says, "Windows XP 64-bit edition has been in development \[as an offshoot of\] a server-oriented build. The market is moving very quickly and mobilizing toward 64-bit on the server as well as the desktop. Initially, we focused on server and technical workstation customers for applications like high-end graphics, CAD, and software development. Over time, we realized that customers are starting to look at 64-bit for much more than a high-end workstation OS. So we decided to provide the full XP feature set."

Initial Problems
Device support is one of two major problem areas for customers testing the 64-bit XP release candidate, which requires 64-bit drivers. According to Marr, "I have an Acer Ferrari \[notebook PC\], and everything works. It comes down to drivers. . .This happens on both desktop and notebook systems—I have a custom desktop in my office and the audio doesn't work... My recommendation would be to wait for a customized version from a vendor—that way you get device drivers specific to the system."

The other major problem area is software compatibility. Although most 32-bit Windows software runs on 64-bit systems, legacy applications written for DOS, 16-bit Windows, or the OS/2 and POSIX compatibility subsystems don't. Neither do kernel-mode applications such as antivirus programs, or applications that incorporate a built-in device driver. According to Marr, Microsoft has been unpleasantly surprised to discover that a few vendors are still shipping 32-bit applications with 16-bit setup software, which doesn't work in the new system. He says that in some cases, Microsoft can provide a "software shim" to get around this problem, but the company is working with vendors to provide proper 32-bit setup software.

According to Marr, the new XP 64-bit edition fully supports key features that notebook vendors require. "Power management and hot dock support are built in. The OEM or IHV has to do some work to make sure appropriate S-levels work. PC Card support is much the same—we provide the necessary infrastructure, but particular drivers may have to be written." And Marr says that a 64-bit XP Hardware Compatibility List (HCL) is on the way: "We're working on it. Windows Marketplace will include a list of logo devices for 64-bit. Our logo program was announced with RC2—it's an addition or option with the current logo. A partner can logo a system, a particular device, or the operating system. And they can logo for either 32-bit, 64-bit, or both."

The Word Is Performance
Why might a notebook PC user want to run 64-bit Windows? In a word: Performance. Using a 64-bit processor such as AMD's Athlon 64 Mobile or Turion 64 CPU theoretically allows twice as much data transfer per CPU clock as a 32-bit CPU. Practically, performance gains are likely to be less than this rate and will depend on software being recompiled for a 64-bit version. 64-bit also allows much more RAM to be used than 32-bit Windows can support—as much as 128GB. Other than that, the new OS is "functionally identical to 32-bit Windows XP," says Marr. "The same features are available, and they can be managed identically through Active Directory. The same scripts and templates apply equally to both 32-bit and 64-bit versions of Windows XP."

Application Availability
When will 64-bit applications be available? Brian Marr says: "It will vary—we will probably see a transition similar to what we saw moving from 16- to 32-bit. Areas where people have already hit the 32-bit memory barrier, including high-end workstation apps, will come first—I expect some in the first three months or so after we ship. . . Later, you'll see more apps moving over—I wouldn't be surprised to see games come over. And then you'll see new apps that are enabled by the 64-bit architecture. Think of things like home video editing that weren't possible in 16-bit but are common today. Think in terms of the Longhorn timeframe for that!"

Marr says that porting 32-bit Windows software to 64-bit, although relatively simple, involves more work than just recompiling. "It's never quite that easy, but it's usually our experience that when people come into our port lab they get things working in a few days and leave with a functioning app." Current 32-bit .NET applications are supported by the .NET Framework version 1.1, and native 64-bit .NET applications will be supported by .NET Framework 2.0, which is now in development.

Windows XP 64-bit edition supports processors that employ the x64 instruction set that AMD introduced in the Opteron 64 processor. This class currently includes AMD's Athlon 64 and Turion 64 processors, as well as Intel's Xeon processor and one version of the Pentium 4 Processor, but not Intel's top-of-the-line Itanium processor.

Hardware Questions
Although notebook PCs capable of running 64-bit XP are available now, it will likely be some time before any vendor will ship a 64-bit Tablet PC or mobile device in a subnotebook form factor, for at least two reasons. First, the current 64-bit version is built from the Windows Server code base. Windows XP Tablet PC Edition 2005 is a superset of the 32-bit XP code base. Second, the power consumption in current 64-bit notebook PCs, which are almost all built with the Athlon 64 processor, is extremely high. AMD's Web site refers to these machines as "desktop replacement" notebooks, and that seems an apt description. According to AMD's technical documentation, the current Athlon 64 CPUs dissipate from 22 to 72 watts of thermal power, depending on the model and operating state. By comparison, Intel's Pentium M Processor—commonly used in 32-bit notebook PCs—dissipates from 4 to 22 watts. Thus, although a 64-bit notebook PC might provide better performance in some applications, it will also have a much shorter battery life than an equivalent 32-bit notebook PC. AMD is addressing this concern with its new Turion processor, which dissipates about half as much power as the Athlon 64, and includes "Power Now" technology that selectively powers down idle components. Nonetheless, it appears that users will pay a penalty in battery life for using 64-bit processors on notebooks for the foreseeable future.

Who Needs It?
Which leaves the question that most readers are doubtless asking: Why in the world would anyone need (or want) a 64-bit notebook PC? The answer, pure and simple, is enhanced power and performance. Brian Marr is quite open about this: "General information workers, honestly, will be better off with 32-bit Windows XP Professional for the foreseeable future. Home users will be better off with 32-bit Media Center or Windows XP Home Edition. We do see a 'fringe' of very high-end users for things like video editing, where in one case we've seen a 15 percent performance gain, even running 32-bit apps. For applications like Office, we see on the order of 5 to 10 percent. For developers, you'd see improved compile time. In cases where floating point, rendering, or computation is critical, you'll see a performance improvement. Windows XP 64-bit Edition is really aimed at a specific group of customers: High-end workstation users, developers, and people who just have to have the latest high-end technology. General business and home users will have a better experience with the 32-bit version for the foreseeable future."

With that said, the early delivery of notebook PCs based on 64-bit technology—and Microsoft's release of a 64-bit OS compatible with them—is certainly an interesting development. IT professionals should expect to see the first 64-bit systems turning up among advanced end users this year.