The years of Moore’s law growth without regard to power consumption are now over. On the data center side, power isn’t close to the largest cost of running a large service but it is one of the largest controllable costs and it has been in the press frequently of late.  On the client side, battery power is the limiting factor. 

It is worth understanding what devices consume the most power since most laptops provide some form of user control.   Most systems allow LCD backlight dimming, the CPU power consumption can be lowered (a combination of factors including reducing clock speed and voltage), wireless radios can be switched off, and disks activity can be curtailed or eliminated.  Where does the power go? 

The data below was measured by Mahesri and Vardhan with an Thinkpad R40 as the system under test:

 Data from: http://www.crhc.uiuc.edu/~mahesri/classes/project_report_cs497yyz.pdf.

The dominant consumer by a significant factor is the CPU.   This power consumption is, of course, very load dependent particularly in multi-core systems where the spread between minimum and maximum power dissipation is even higher. The second largest consumer is the LCD backlight, which isn’t surprising.  Two LCD-related findings that I did find surprising: 1) the LCD without backlight is a very light consumer of power, and 2) there is a perceptible difference in power consumption between mostly black and mostly white backgrounds.   The hard disk drive power consumption was notably less than I expected with only 2.8W dissipated during active reading.

I wrote up more detail in: ClientSidePower6_External.doc (130 KB).

                                                 --jrh

James Hamilton, Windows Live Platform Services
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