Among the “specific Windows 7 improvements,” the company enumerated the elimination of the “TCP DCP timer on every system timer interrupt, reducing the frequency of USC driver maintenance timers, Intelligent Timer Tick Distribution, Timer Coalescing,” via the “Windows 7 Power Management Overview”.

Reduced Power Consumption might be a reason to consider an upgrade to WS 2008 R2.  Windows Server 2008 introduced a 'balanced' power policy, which monitors the utilization level of the processors on the server and dynamically adjusts the processor performance states to limit power to the needs of the workload. Windows Server 2008 R2 enhances this power saving feature by adding CoreParking and expanding on power-oriented Group Policy settings.

Download: Win7 Power Management / WS 2008 Power Management (.PPT)

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