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CPU/VRM Power Consumption
To get an idea of how much power the CPU actually requires, we measured the
current (through a 0.01 ohm shunt resistor) and voltage at the ATX12V connector in various CPU load states. This allows us to calculate the power demanded by the CPU and the board's VRM (DC-DC converter).
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DC Power Consumption
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Test State
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Core i5-661 @ 3.33GHz
(Stock)
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Core i5-661 @ 2.26GHz (Underclocked)
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System
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CPU + VRM
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Diff.
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System
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CPU + VRM
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Diff.
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Idle
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18W
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5.3W
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12.7W
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18W
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5.2W
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12.8W
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CPU Load
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60W
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46.0W
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14.0W
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45W
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32.4W
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12.6W
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CPU + GPU
Load
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67W
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51.2W
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15.8W
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54W
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39.0W
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15.0W
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CPU Load (Turbo)
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63W
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48.0W
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15.0W
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N/A
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CPU Load + GPU Load (Turbo)
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69W
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52.7W
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16.3W
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N/A
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CPU + VRM power measured from the ATX12V connector
(combined DC draw of VRMs and CPU).
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By our measurements, our i5-661 sample used 5.3W when idle and up to 46.0W
when stressing the CPU with Prime95, with an indeterminate amount lost to VRM
inefficiency. The addition of FurMark's GPU stability test resulted in an additional
5.2W draw.
Between 13W and 16W was used by the rest of the system which consisted of the
motherboard, two sticks of memory, a notebook hard drive, idle Blu-ray drive,
keyboard and mouse.
System Power Consumption Comparison
To compare the Core i5-661 to other processors we've tested, we changed the
hardware to match our CPU testing platform, swapping the notebook hard drive
for a Velociraptor and using a GeForce 9400GT rather than integrated graphics.
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Test Results: System Power Consumption (DC)
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Processor
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Idle
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VC-1
Playback
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CPU
Load
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C2Q Q9550
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47W
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57W
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115W
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Core i5-750
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37W
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55W
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107W
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Core i5-661
(Turbo)
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31W
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45W
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79W
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Core i5-661
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31W
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45W
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78W
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C2D E7200
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41W
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50W
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69W
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X4 955 BE
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56W
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79W
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171W
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X3 720 BE
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58W
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77W
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127W
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X2 550 BE
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48W
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67W
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106W
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Back in September we reviewed the Core i5-750 and i7-860 Lynnfield quad core
processors and found them to very energy efficient. The i5-661, utilizing a
smaller manufacturing process and half the cores is even more thrifty when it
comes to power draw. Power consumption was 10W less than the Core 2 Duo E7200
when idle and only 10W more on full CPU load. AMD's fastest dual core, the X2
550 Black Edition, an 80W chip, was off the mark by 20~30W.
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