Also propelling the move is the trend toward server consolidation. One option for that is virtualization, which allows multiple OSes and application loads to run on a single physical machine, and server virtualization requires the capacity of a powerful, 64-bit server.

"Anybody doing a deployment today would be foolish not to at least consider when and where a 64-bit OS would be a good fit," said Al Gillen, a research vice president with IDC. "It's really about future-proofing your IT environment, giving yourself the ability to support the workloads that you'll have on these servers before they are retired in five years' time."

IDC has called the lack of adoption of 64-bit Windows Server "one of the biggest missed opportunities among today's customer base." It notes that the 64-bit products will be priced the same as their 32-bit counterparts and argues that the transition is relatively easy for customers.

The 64-bit processors from Intel and AMD have maintained the x86 architecture from the 32-bit world. That means 32-bit applications can still run on 64-bit servers, and that "the majority of existing 32-bit applications will run aboard 64-bit Windows Server without modification and, most frequently, with improved performance," IDC said.

Customers will need to update low-level system tools such as security products, antivirus tools and some system-management products, which interact directly with the Windows Server kernel, IDC said.

At the end of 2007, the research company estimates, only about 10 percent of Windows Server customers were using the 64-bit edition of Windows Server 2003. It expects that figure to approach 50 percent by the end of 2010, driven by Windows Server 2008. For new licenses sold in 2010, close to 75 percent will be for a 64-bit version of Windows Server, IDC said.

Microsoft is keen to promote the transition to 64 bits. It will give its customers better performance and help Microsoft catch up with the Unix world, where powerful, but more expensive, servers from Sun, IBM and HP have long been based on 64-bit OSes. Microsoft believes the products launching this week will mark "a big turning point" toward the use of 64-bit Windows software, said Ward Ralston, a Microsoft senior technical product manager.

Microsoft also is pressuring ISVs (independent software vendors) to get their software 64-bit ready, after a lack of preparedness held back the transition after Windows Server 2003 was released. ISVs aren't required to have a native 64-bit edition of their software to receive a Certified for Windows Server 2008 logo, but they will need to assure their software can run on the 64-bit OS.