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TEST RESULTS
Our test systems consist of 2x2GB of DDR3 memory (1333 MHz, 9-9-9-24-1T timings),
a GeForce 9400GT graphics card, WD VelociRaptor hard drive and an OEM Seasonic
power supply. Turbo Boost was disabled during testing — we consider it overclocking.
The ambient temperature was 21-22°C.
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Test Results: General System Power Consumption (AC)
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Test State
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i7-965
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i7-870
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i5-750
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QX9650
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Q9550
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X4 955
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Idle
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84W
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54W
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52W
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68W
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64W
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73W
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VC-1
Playback
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100W
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72W
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72W
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86W
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75W
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99W
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CPU Load (half cores)
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145W
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104W
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96W
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122W
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120W
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157W
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CPU Load (all cores)
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203W
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147W
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130W
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142W
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140W
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201W
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The new Lynnfield processors impressed us immediately after general power consumption
tests. Compared to LGA775, the LGA1156 configurations used about 10W less less
power in idle and during VC-1 video playback, and approximately 20W less when
two of the four cores were stressed with Prime95. With wattage numbers in the low 50's,
they rival some dual core processors in idle power draw. The Core 2 Quads were
already very energy efficient, and i7-870 and i5-750 proved to be even more
frugal.
The power draw of the two Lynnfields were similar — nothing but negligible
differences were noticed until the CPU was stressed heavily. With two cores working
at their maximum, the 870 used about 8W more. The difference more than doubled
to 17W when all four cores were taxed.
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Undervolted Test Results: General System Power Consumption
(AC)
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Test State
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i7-870
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i7-870
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i5-750
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i5-750
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QX9650
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Q9550
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Stock
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UV
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Stock
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UV
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Idle
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54W
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53W
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52W
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48W
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68W
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64W
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VC-1
Playback
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72W
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69W
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72W
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67W
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86W
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75W
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CPU Load (half cores)
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104W
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94W
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96W
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85W
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122W
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120W
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CPU Load (all cores)
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147W
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128W
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130W
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110W
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142W
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140W
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i7-870 undervolted to 1.025V stable (~1.1375V stock).
i5-750 undervolted to 1.0625V stable (~1.1625V stock).
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Undervolting yielded further gains in energy efficiency. We managed to get
the 870 semi-stable (10 minutes of Prime95) at stock speed with 1.025V in the
BIOS. The 750 required 1.0625V. This resulted in slightly less power draw
in idle and during VC-1 playback, saved 10W when two cores were stressed
with Prime95, and 20W with all four cores under load.
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CPU screenshot: i7-870 undervolted to 1.025V. CPU-Z reported 0.768V when
idle (1.2 GHz).
CPU screenshot: i57-750 undervolted to 1.025V. CPU-Z reported 0.704V when
idle (1.2 GHz).
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