In this day and age, power use is on everyone's mind. Windows Server 2008 R2 helps reduce and optimize power usage in most, if not all, situations; in all cases, savings can be achieved and realized simply by installing the operating system.
Perhaps the easiest savings to point to when upgrading to Windows Server 2008 R2 is in power management. In essence, on the same hardware with the same load factors, Microsoft claims R2 will present anywhere from 10% to 15% -- and sometimes even 18% -- power savings over Windows Server 2003 with Service Pack 2, without requiring any additional configuration.
The largest area of savings is on a server at idle load, thanks mainly to improvements in driver tuning and power management in hardware that can be used by the OS. However, even after loads begin to creep up, clever OS management features can maintain a significant reduction in power consumption. This is made possible through a rewritten processor power-management engine and enhancements to storage power management, among other features. Hyper-V 2.0 is also able to harvest most of these power-savings improvements, making the power story a compelling one for companies with data centers approaching capacity in terms of space and power.
Core parking is another interesting feature that intelligently detects loads on a system and prioritizes and optimizes the distribution of that processing workload among all of the cores available to the operating system. For instance, on single quad-core processor, core parking will enable modest workloads to be carried out only on one core and allow the remaining three cores to remain in a power-saving inactive state. When workloads become heavy enough to require the use of other cores, the OS "lights up" the other cores as necessary to handle the duties, and then returns them to the inactive state -- creating, in other words, a "bursting" of processor capacity.
The ability to detect power use and act on that is something new to Windows, and Windows Server 2008 R2 adds power consumption and budgeting information reporting features. Unlike some of the other out-of-the-box features, reporting and budgeting require the server hardware to play along. The hardware itself reports power information via the Advanced Configuration and Power Interface (ACPI) to the operating system, and Windows then exposes that information through Windows Management Instrumentation (WMI) -- including all plan and setting data. Whatever power plan is created can be administered remotely, and whatever existing power-management settings you may have in R1 also can be administered remotely.
Along with this comes the power budgeting feature, useful in certain scenarios where you want to cap the amount of power used by systems. Windows can intelligently control the power use of every device on supported systems, down to the device level in some cases, and establish a "governor" on power use that can be very useful in power-limited situations. For manufacturers, there is a Windows Driver Model (WDM) driver interface available for power budgeting.