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Power
The power consumption of an add-on video card can be estimated by comparing
the total system power draw with and without the card installed. Our results
were derived thus:
1. Power consumption of the graphics card at idle - When CPUBurn is
run on a system, the video card is not stressed at all, and stays in idle mode.
This is true whether the video card is integrated or an add-on PCIe 16X device.
Hence, when the power consumption of the base system under CPUBurn is subtracted
from the power consumption of the same test with the graphics card installed,
we obtain the increase in idle power of the add-on card over the
integrated graphics chip (Intel GMA950). (The actual idle power
of the add-on card cannot be derived, because the integrated graphics does draw
some power — we'd guess no more than a watt or two.)
2. Power consumption of the graphics card under load - The power draw
of the system is measured with the add-on video card, with CPUBurn and FurMark
running simultaneously. Then the power of the baseline system (with integrated
graphics) running just CPUBurn is subtracted. The difference is the load power
of the add-on card. (If you want to nitpick, the 1~2W power of the integrated
graphics at idle should be added to this number.) Any load on the CPU from FurMark
should not skew the results, since the CPU was running at full load in both
systems.
Both results are scaled by the efficiency of the power supply (tested
here) to obtain a final estimate of the DC power consumption.
|
Estimated Power Consumption Comparison (DC)
|
|
Card
|
Idle
|
Load
|
|
Asus GeForce 9400GT 512MB
|
11W
|
23W
|
|
PowerColor HD 4650 512MB
|
15W
|
28W
|
|
ATI HD 4830 512MB
|
18W
|
87W
|
|
PowerColor HD 5850 1GB
|
21W
|
132W
|
|
ATI HD 4770 512MB
|
28W
|
60W
|
|
Asus GTX 260 896MB
|
35W
|
145W
|
|
ATI HD 4870 1GB
|
67W
|
134W
|
|
HIS HD 4890 Turbo 1GB
|
71W
|
149W
|
We've criticized ATI in the past for the relatively high idle power consumption
of their graphics cards when compared to Nvidia's offerings, but the HD 5000
series seems to have finally knocked out that particular problem. The HD 5850
uses about 21W when idle, a massive reduction compared to the HD 4890, impressively
low for a high-end video card. ATI also managed a small reduction on load which
is also admirable when you consider than its supposed to be 20~30% faster than
the HD 4870/4890.
Video Playback
|
Test Results: Video Playback
|
|
Test State
|
Average
CPU Usage
|
Additional
DC Power*
|
|
Rush Hour
(1080p H.264)
|
5%
|
+25W
|
|
Coral Reef
(WMV-HD)
|
27%
|
+44W
|
|
Undead Battle
(720p x264)
|
4%
|
+22W
|
|
Spaceship
(1080p x264)
|
3%
|
+22W
|
|
*compared to idle
|
The HD 5850 passed our video playback test with flying colors, with H.264 and
x264 playback adding only 25W and 22W respectively to DC system power, much
of which can be attributed to the GPU as CPU usage was very low. Our WMV-HD
clip required more CPU cycles and we noticed a bug: the core and memory clocks
of the graphics card increased to the maximum 700/1025Mhz setting rather than
the UVD speeds of 400/900MHz. As a result, the total system power draw increased
by 44W, which is unusually high.
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