A. Server 2008 R2 introduces the ability to put certain cores on processors to sleep if the system load doesn't warrant all the cores running. To view the core sleep state, you can use Performance Monitor and view the Processor Information, Parking Status counter for each core instance.

It's impressive how many cores are put to sleep at any one time. Below you can see a dual core box. Basically, at any time one of the cores is always asleep. I recommend changing the scale to 2 for easy viewing (viewing a value of 0 or 1 on a scale of 100 is difficult). Right-click the graph, select Properties, and on the Graph tab change the maximum value for the vertical scale.

Performance Monitor with two cores

On my 16-core box (eight hyperthreaded cores), you can see that many of the cores are asleep. By looking at the Average value for each instance we can see what percentage of the time a core is asleep.

Performance Monitor with 16 Cores