Skybuck said:
You have to know how to interpret those figures.
One of those figures is "magic" and someone needs
to translate it into English.
The figure I quoted, is extracted from here.
http://www.gpureview.com/GeForce-GT-520-card-650.html
and is the same 29W as your Geforce (Nvidia controlled) website.
So this value, is the value provided by the manufacturer.
http://www.geforce.com/hardware/desktop-gpus/geforce-gt-520/specifications
*******
This page, requires a modern browser to render properly.
http://www.asus.com/Graphics_Cards/ENGT520_SILENTDI1GD3LP/specifications/
Power Consumption
up to 75W
no additional PCIe power required
Now, that 75W value is the limit of the PCI Express motherboard
connector. In other words, if you draw 76W with a high end video
card, the edge connector (in theory) would burn up. The number is based
on the number of contacts in the PCI Express slot, in the power
delivery section of the connector.
A video card, with no AUX connector on the end of the card,
is limited to using 75W, as provided by that connector.
The video card in question, the GT520, *actually* draws 29W,
well below the 75W limit.
So Asus is saying, "we don't know the real actual power,
but our marketing people can tell you the power must
be less than 75W, because there is no AUX connector on
the end of the card".
So the power number for the card, remains at the 29W
value I quoted.
As an engineer, I always do "sanity check" on power
calculations. Say a power calculation gave 1000W dissipation,
on a device that fit in the palm of my hand. Common sense
tells you the object would be "incandescent" if it
dissipated 1000W. So any time you receive conflicting
information, look at the heatsink. "Does that heatsink
handle 29W ?" "Does that heatsink handle 75W ?". If
you look at the heatsink, the physical size and surface
area and fan size and fan speed, can give a hint as to
actual power.
I'm willing to bet, if Xbitlabs.com measured the power
for the GT 520, they would find a value of *less* than
29W. They equipped a couple motherboards with current
measurement shunts, so that they could measure the
current flow in the edge connector. Measuring one card
is not statistically significant (does not establish
the mean value), but it can shine some light on
the absurd manufacturer number. The manufacturer numbers
(29W) are normally, too high.
Modern cards have things like "power limiter" in the
design, to cap the tails of the 3sigma power distribution.
At one time, the video card you bought, could have a higher
power dissipation than the one I bought. And this is
statistical variation. (This is also affected by the
OEM video card manufacturer overclock setting and
VCore choice for stability.) But with some of the
modern designs they have power limiters, if you run
Furmark, the card "throttles" itself, if you attempt
to draw too much power. So rather than having a
fixed computation rate of 512 shaders at 1000MHz,
the computing rate is fixed by when the power regulator
says "you're drawing too much power" and the clock
rate drops in response.
*******
GT 520 = 29W
Still true.
Until Xbitlabs measures it, and gives us an even *lower* number.
Paul
