ZOTAC GeForce GT 640 ZONE Edition Fanless GPU

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TEST RESULTS

Baseline Power with Integrated Graphics:

Power Consumption Measurements:
GPU Test System (Intel HD 2000 IGP)
Measurement
Idle
CPU Load
CPU + GPU Load
Sys. Power (AC)
36W
74W
87W
Sys. Power (DC)
unknown
61W
72W
System fan speeds: Low
Ambient noise level: 10~11 dBA
System noise level: 12~13 dBA

System with Discrete Graphics:

System Measurements: GPU Test System
(ZOTAC GeForce GT 640 ZONE Edition)
State
Idle
CPU Load
CPU + GPU Load
Temp
CPU
24°C
36°C
42°C
38°C
35°C
PCH
44°C
44°C
46°C
46°C
43°C
GPU
38°C
39°C
99°C*
98°C
89°C
System Fan Speed
Low
Med
High
SPL @1m
12~13 dBA
18 dBA
26 dBA
Sys. Power (AC)
45W
85W
122W
121W
121W
Sys. Power (DC)
unknown
70W
107W
106W
106W
Ambient noise level: 10~11 dBA
Ambient temperature: 22°C

With our test system fans on our low speed, 12~13 dBA@1m setting, the GT 640 ZONE Edition ran fairly cool and was also very energy efficient with only 45W being pulled from the wall outlet. On load, the GPU temperature gradually climbed until it reached 99°C and then suddenly leveled off even though the rate of temperature increase hadn't really slowed at that point. It stayed at 99°C indefinitely but we assume this was a bug and that the actual temperature topped 100°C. Interestingly, the card remained stable during this time..

In any event, 99°C was still fairly hot so we increased the system fan speed to the medium setting (18 dBA@1m). After a few minutes the GPU temperature sensor started responding again, dipping down to 98°C. It took our high speed setting (26 dBA@1m) before it dropped to the reasonable temperature of 89°C.

It was a disappointing result — If you need to crank up your system fans to achieve a decent level of cooling, it negates much of the advantage of having passive heatsink. To be fair our test is more stressful than any real world situation but it can come close depending on the climate and other system components. Either way, we can't recommend using this card in a very quiet or close to silent system with minimal airflow. It needs a little help or it will become quite toasty on load.

Power Consumption

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 Prime95 is run on a system, the video card is not stressed at all and stays idle. 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 Prime95 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.

2. Power consumption of the graphics card under load — the power draw of the system is measured with the add-on video card, with Prime95 and FurMark running simultaneously. Then the power of the baseline system (with integrated graphics) running just Prime95 is subtracted. The difference is the load power of the add-on card. 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.

Note: the actual power of the add-on card cannot be derived using this method because the integrated graphics may draw some power even when not in use. However, the relative difference between the cards should be accurate.

According to our calculations, the GT 640 ZONE Edition consumed about 9W when idle and 45W on full synthetic load, about the same as the Sapphire HD 7750 Ultimate. 9W idle is fairly impressive, edging out most of the low-end AMD cards we've tested in the past.

All of the AMD/NVIDIA cards from the last three generations had very similar CPU usage during video playback, 1~2% for our 1080p H.264/MKV test clip, and 8~9% for our YouTube HD sample. Power consumption however varied greatly, dependent mostly on the core/memory clocks used by the cards' respective video decoder chips. This favors the NVIDIA cards as most of them utilize much lower clock speeds.

The GT 640 is among the most frugal cards when playing video, increasing the system power consumption by only about 5W. Add this to its already low idle draw, and it's an impressively efficient GPU for a media PC.



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