I've been playing around with Windows XP Professional x64 Edition on an AMD64 clone and although I'm having fun with it, I haven't decided whether I'm in love. You see, I ran 64-bit Windows (well, sort of) 6 years ago, and there are definitely elements of deja vu all over again. I used the version of Windows NT 4.0 that Microsoft produced for a chip called the Alpha, which Digital Equipment created to drive a line of servers and high-end engineering workstations. I used one of those workstations as a server in my small network, so perhaps I can provide a preview of what running this new flavor of Windows might be like.
Over the years, Microsoft has offered NT for a variety of processors other than the Intel x86 architecture; we've seen MIPS, PowerPC, and Alpha versions of NT. Because NT wasn't strongly wed to any one architecture, you could easily move it to whatever chip was reasonably priced and popular. Although it was certainly convenient to be able to run a familiar OS on the Alpha, just having Windows on it didn't automatically make it as useful as an Intel box running Windows--Alpha had its problems.
Applications presented a major stumbling block. Programs compiled for the x86 processor use machine code that called processor instructions that don't exist on an Alpha. That meant you couldn't simply copy winword.exe from an Intel box to an Alpha box to get a working version of Microsoft Word on an Alpha--you need the original Word source code (or you could wait and hope that Microsoft would compile a version of Word that ran on an Alpha). Few application vendors compiled their programs to run on the Alpha, so few applications existed for the platform, which likely led to its ultimate demise. Digital developed a technology called FX!32 that was intended to solve this compatibility issue, but it never worked well enough to solve the problem.
The good news is that users of modern 64-bit processors such as AMD's 64-bit CPUs won't need to worry about application compatibility because AMD's chips run both the older x86 opcodes and the newer 64-bit opcodes. Therefore, most standard 32-bit Windows applications will run on x64 Windows. However, 16-bit Windows applications won't run. You probably won't care, except for situations in which an application uses a 16-bit Setup program--and believe it or not, a few still exist. And of course, no DOS programs will run.
DOS applications gave the Alpha real heartburn. The Alpha lacked the x86 instruction set, so Microsoft added an early version of what eventually became Virtual PC, which emulated an entire x86 environment. XP Pro x64 simply refuses to run any DOS applications. (From what I've read about the kernel's architect, Dave Cutler, he hates DOS applications, and it's hard to disagree with him. Cutler must be overjoyed at finally extirpating DOS from Windows.) To work around the DOS problem, I used VMware's VMware Workstation 5.0 to create a virtual machine (VM) that ran DOS applications.
Drivers presented another compatibility headache for my Alpha system. It was a screamingly fast system (for its time), built for high-speed graphics, and it came with a fast video board and drivers. Although the Alpha used PCI slots and so, in theory, could accept thousands of add-in cards, almost none had Alpha drivers. Will x64 users see similar problems? Perhaps. I had difficulty finding a driver for my computer's Ethernet card, an NVIDIA chip that's been a headache since I got the box. But I did find a driver, although NVIDIA calls it a beta driver.
But don't let me paint the driver picture all black. Drivers on XP Pro on an x64 machine are a much different story than drivers on NT 4.0 on an Alpha. First, XP has Plug and Play (PnP) technology, so making drivers work is much easier. Second, many devices can use a generic driver. For example, if x64 doesn't have a driver for your digital camera but the camera connects via USB, the generic USB storage driver might work. A driver for your printer might not exist, but a driver from an earlier model might support some or all of your printer's features. The most likely driver irritation will be video drivers and video capture. To work around the video capture problem, I run the video device that I want to capture from through FireWire because x64 thankfully has drivers for my FireWire hardware.
I hope Microsoft addresses the problem of video drivers. I suspect that in 2 years, most of the people that buy x64 will do so for its video capabilities--faster games, for example. I predict that we'll soon see some neat games for the x64 platform, given how inexpensive AMD64 hardware is. In my case, I'd like a video-editing tool that exploits x64's massive (16TB) virtual memory space. The video-editing applications that I've used are wobbly and prone to crashing. I'm hoping that a bit of elbow room (i.e., elbow RAM) will make that instability a thing of the past.
The Alpha was a great computer to work with despite its problems. It offered a familiar NT 4.0-type interface and all the tools that came with x86 NT (e.g., Control Panel, Network Neighborhood, Notepad, Calculator). But running them on the Alpha was like seeing them anew--they were so incredibly fast!
That gee-whiz factor won't translate for users who have AMD64 hardware. I had to run special Alpha software to appreciate the Alpha's speed. I don't have to do that with the AMD64 because it runs regular 32-bit XP without a problem.
Does putting 64-bit Windows on your workstation make sense? In the long run, I think yes, albeit as a second OS. The world is heading toward 64-bit: quickly in the server world, much slower in the laptop world, somewhere in between in the desktop world. NT has always suffered from a few built-in limitations in terms of how kernel memory is laid out, and moving from the x86's 4GB memory space to the AMD64's 128GB memory space let x64's designers give the OS a bit more breathing room. Granted, most of that extra memory will benefit server builds more than desktop builds, but I won't be surprised if in a few years new 32-bit hardware is difficult to locate. It can't hurt to get comfortable with 64-bit Windows now. And if you do decide to try out 64-bit computing, I recommend that you do as I did and install XP Pro x64 on a second hard disk in your system. I don't yet trust 64-bit versions enough to close the door forever on 32-bit desktops.