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 will 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 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 that their software can run on the 64-bit OS.

Some expect Microsoft's virtualization technology, Hyper-V, to be a factor. The hypervisor will be offered free with the 64-bit edition of Windows Server 2008. Andrew Brust, head of new technology for the IT consulting company Twentysix New York, a Microsoft partner, said that Hyper-V "once it ships, is going to be huge. The virtualization space is ripe for some new competition."

Brian Randell, a senior consultant with another Microsoft partner, MCW Technologies in Los Angeles, said Hyper-V will be a major impetus for the move to 64 bits. "It demands that you have that kind of processor environment available," he said.

However, others pointed to Hyper-V's immaturity. It was originally planned to ship with Windows Server 2008 but has been delayed for up to six months. Even then it will be Microsoft's first attempt at virtualization, noted Michael Cherry, an analyst at Directions on Microsoft.

"I think there's too much emphasis on virtualization with this release," he said. Hyper-V may eventually play a significant role for Microsoft, but the company first needs to develop the required tools for managing a complex virtualized environment. After the hypervisor is released, he said, Microsoft will also need to update its Virtual Machine Manager product.

Still, Cherry is upbeat about the new products, particularly Windows Server 2008. The redesign of the OS to allow customers to install only the functions they need for particular tasks, or roles, will provide security and maintenance advantages, he said. He also pointed to the new Internet Information Server, which gives more options for running and controlling applications remotely, and a significant update to Terminal Services, which will make it easier to run line-of-business applications on a server and make them appear to the end-user as if they were running locally.

Twentysix New York's Brust said the new server products are "rock solid on 64-bit, and so too are the currently shipping versions of SQL Server, SharePoint and other server applications."

"When SQL Server 2008 ships, it will be the third version of the product to offer 64-bit support," Brust said. "Let’s face it, it’s time to move off 32-bit."