In 2003 AMD released the Opteron and followed it with the Athlon 64, bringing the dream of 64-bit computing to the masses. The dream would mean the end of the 4 GB memory limit, as well as other potential performance benefits.
Fast forward to mid-2007, and 64-bit is still the other flavor of Windows. So what’s holding 64-bit back on the windows side? Drivers for one:
“Several issues have contributed to the problem, but as seen in other transitions, device drivers always seem to be front and center. Drivers are a vexing piece of the PC puzzle. They're small bits of software needed to make sure devices like printers, DVD drives and graphics cards connect properly to PCs and Macs, and they can cause major problems if something goes wrong.
Microsoft is requiring those device manufacturers to develop 64-bit drivers if they want their devices to work with the 64-bit edition of Windows Vista, in an effort to ensure that device drivers are written to proper standards. But hardware vendors and application developers haven't wanted to take the time and effort to develop new software for an operating system that very few people use. As a result, 64-bit Windows software is hard to find, although Microsoft says the situation is improving.”
Apple has been taking a different approach with Tiger and Leopard. Both could be considered pseudo 64-bit OSes because they allow 64-bit programs to take advantage of larger amounts of memory and use 64-bit instructions while simultaneously running stable 32-bit drivers.
It is entirely possibly that Microsoft might follow a similar approach. Early reports on the next major Windows release, dubbed 7, indicate that it might continue to follow the 32-bit and 64-bit flavors. On the other hand, it's entirely possible that such rumors will prove unfounded or that Microsoft will rethink their current approach.
It might take a major push from Microsoft to move the entire industry over to the 64-bit. We'll keep our fingers crossed that it comes sooner rather than later.