From a Server perspective, Power Management, Virtualization, and Greater than 64 processor support are considered the top three features for Windows Server 2008 R2 among the announcement at PDC and WinHEC conferences. I will focus on the greater than 64 processor support, given it is a new milestone for Windows, and sets up the stage for competing on much larger and higher end servers.  The support enables large scale database customers to deploy their solutions on Windows and expect good scalability numbers.  Of course, the scalability realized is highly dependent on the applications and drivers being able to scale well beyond 64 processors.  To do so, application and driver developers are strongly encouraged to read up on the greater than 64 processor work to see what has changed, and what type of code modifications are necessary to take full advantage of this new capability.  The document describes the architecture, terminology, and goes into more details about the new APIs.

Source:→ Windows Server Team