Quad/Octo core: How many watts are Actually used?

[SLT]

I’m still undecided whether to get the Mac Pro with one or two 2.8 GHz processors. One of the factors I take into account is how many watts the machines use. The TDP of these processors is 80 Watt. Two processors would make a maximum of 160 Watts.
But lets say that at a certain point in time, I would be reading my email only. Not a processor intensive task at all. How many watts would be used then, when you would compare the dual processor to the single processor? Would the processor-part of a dual processor Mac use twice as much electricity, because two Xeons sit in it? Or would it be less, because the task I’m performing is not processor intensive?
Could someone please shed a light on this?

 

[newtech]

TDP is the design target HEAT output, actual power consumption is higher as not all the consumed power is directly converted to heat.

Example

Assuming 60% of power consumed does actual work, 80 Watts represents the 40% of the power that becomes waste heat.

 

[Pressure]

Indeed, Thermal Design Power indicates the amount of heat a certain cooling solution is required to dissipate.

 

[Umbongo]

http://www.extreme.outervision.com/psucalculatorlite.jsp has the new Intel processors in, it may be of some use to you. Also worth noting that the 80W TDP is a rating, not the exact number.