"Why the change? The natural evolution of the x86 64-bit architecture has led to the creation of processors and servers which deliver the scalability and reliability needed for today's "mission-critical" workloads," wrote Dan Reger, senior technical product manager for Windows Server at Microsoft in a blog entry.

Intel's Poulin said the OS was installed in less than 5 percent of Itanium servers, and it didn't make commercial sense for Microsoft to continue support, he said.

Intel is now trying to refocus Itanium to differentiate it from its x86 processors. Itanium will be targeted at systems running the HP-UX OS and at "select mainframe markets" based on Unix and other operating systems, said Rob Shiveley, Intel's mission-critical platform marketing manager. Xeon chips will be for mission-critical servers running the Windows, Linux and Solaris operating systems.

Intel will also continue to invest and develop new Itanium processors, which will be released in two-year increments, an Intel spokesman said. The company in February released the latest Itanium processor code-named Tukwila, which will be followed by Poulson and then Kittson.