Why the change? "The natural evolution of the x86 64-bit ("x64") architecture has led to the creation of processors and servers which deliver the scalability and reliability needed for todays "mission-critical" workloads. Just this week, both Intel and AMD have released new high core-count processors, and servers with 8 or more x64 processors have now been announced by a full dozen server manufacturers. Such servers contain 64 to 96 processor cores, with more on the horizon," Dan Reger, Senior Technical Product Manager Windows Server wrote at the Windows Server division blog.
Windows Server 2008 R2 was designed to support the business-critical capabilities these processors and servers make available. It supports up to 256 logical processors (cores or hyper-threading units), so its ready for the ever-increasing number of cores. It supports technologies such as Intels Machine Check Architecture, which allow for the detection and correction of bit-level hardware errors. And NEC just published a new world record TPC-E benchmark for online transaction processing of 3,141.76 tpsE on a system with 8 x64 processors a result more than 50% higher than the previous record.
Microsoft said that it would continue to focus on the x64 architecture, while they continue to support its Itanium customers for the next 8 years as this transition is completed.