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- Power supply calculator: accurate?
January 20, 2006, 8:01 am
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Re: Power supply calculator: accurate?
CPU - didn't take Vcore efficiency into account. CPU should be
at least 10% higher than listed.
Video card - Xbitlabs has a number of articles, where they've measured
video card power. Those results should be added to the
table of cards. Xbitlabs even breaks down to amps per rail.
Memory - DIMM power ratings are not additive. The second to nth DIMM
on a channel draw "idle" power, for calculation purposes.
So this tool will overestimate memory power (but perhaps not
as bad as it did in the past).
Hard drive - 11W is a typical idle power these days. Overestimated.
- If you are building a server, then all disks are busy.
- tool does not account for spinup, which is not an issue
unless you have a large number of disks. Stopping at
four disks is actually a good thing for this tool, as
Optical - No real data available, boiler plate ratings are pessimistic.
There is no way to improve this section, unless someone takes
10 minutes with a clamp-on DC ammeter and measures it.
USB - 5V@500mA max is 2.5W, not 5W.
Firewire - meaningless for estimation purposes. Plugging a DV camera
draws no current.
The tool should work out the output currents for +3.3V, +5V, +12V,
so the user can buy a power supply with the right balance of outputs.
Buying power supplies based on "total power" is not really that
meaningful. If the tool said I needed 150W, would a 500W supply
with a 12V@10A rating be good enough ? (the answer is quite likely
to be "no"). The tool leaves you guessing.
I like the approach of this tool better, but this tool doesn't have
any info on modern hardware.
I think there is room for another web site to take a crack at
designing a tool. A spreadsheet approach would make it more obvious
as to how they arrive at the numbers, especially if the tool
provides some refinements on how some device powers add. Correlating
the tool calculations, with some real measured systems, would add
immense value to such a tool, as then people could see how far off
the method is, when compared to a "reference system". Any of the
hardware review sites, get to see enough hardware, to make such a
collection of information easy.