Oh and BTW here is the article.
I actually wrote more than that, but I cant seem to find it. Sorry 'bout the long post
At 09:16 PM 5/02/2010, Jeremy (xxxxx) wrote:
>Me and my friend were having this little debate the other day. He
>thinks that you need atleast a 650w Power Supply to power and
>average gaming system. Apparently any 650w will do. He even picked
>out an Apower 650w for me!
There's no way to put a definite figure on the power consumption of
an "average gaming system", because there are many possible
configurations for such a system.
A computer like the one you describe, though, shouldn't be able to
draw more than about 300 watts no matter what you do to it. Maybe
400, if you really push for some overclocking records.
But that doesn't mean that a "300W" PSU will be able to power it,
un-overclocked, perfectly. For three reasons.
One: The current draw of your computer on the different PSU rails
probably won't perfectly match the current-rating division of those
rails on the PSU. Modern PCs generally need a lot of amps on the 12V rail.
Two: Even high-quality PSUs aren't made to deliver something close to
their maximum rating for long periods of time.
Three: Most PSUs are not high-quality PSUs.
An awful lot of PSUs aren't even _fair_-quality; they can't deliver
anything remotely LIKE the wattage number on the sticker.
A decent "650-watt" PSU certainly should be more than enough for the
Core i5 system you describe. An A-Power "650W" PSU might be OK, or
might not; A-Power appear to be just one among many anonymous rebadge
brands clustered at the front of the cheap-hardware phone-book.
(That's if the A-Power you're looking at is the same A-Power I see,
with PSUs in the 700-to-900W range... for fifty bucks. Yeah, right.)
There's a reason why one "650W" PSU costs $50 and another costs $200.
The more expensive one will probably weigh a lot more, last rather
longer, be made in a much more reputable factory, and be able to get
a lot closer to its sticker capacity.
At the very bottom end of the market there are PSUs that come from
the factory with no power rating sticker on them at all. The retailer
just sticks a "400W" sticker on the box if he wants to sell it as a
400W PSU, or a "700W" sticker if he wants to make a bit more money.
Your typical dirt-cheap allegedly-500W no-name PSU today can
confidently be expected to be good for not much more than 250W (
http://www.hardwaresecrets.com/article/534/5
), and even at that load
level it'll probably only survive a few weeks.
Fortunately, magazines like Atomic and all of the major review sites
are well aware of this problem, and do proper load tests. This makes
it quite easy to find the PSUs with honest ratings.
(There are a lot more PSU brands than there are PSU factories. A few
top-flight factories, like "Channel Well Technology" for instance,
make PSUs for several big brands. CWT make (or have made)
Thermaltake, Antec and Corsair PSUs, among many others - check out
http://tinyurl.com/psumakers
http://www.jonnyguru.com/modules.php?name=NDArticles&op=Story&ndar_id=24
for a not-recently-updated list of many of the myriad brands in just
the more honourable section of the PSU market.)
PC power consumption is, as you'd expect, usually dominated by CPU
and graphics-card wattage. It's pretty easy to get even low-end CPUs
to draw a big old slab of watts by overclocking; power consumption
increases directly with clock speed, but also with the _square_ of
any voltage increase you have to use to get an overclock to work. So
if you increase voltage by 10% to get a 20% overclock, power
consumption increases by a factor of 1.1-squared times 1.2, or 1.45.
The Thermal Design Power (TDP) for the Radeon HD 5770 is 108 watts.
No Core i5 CPU so far has a TDP above 95 watts.
The TDP is the most power a component is supposed to ever draw for
any length of time. It's the power number that's used when designing
the cooling system for the computer. You can squeeze CPUs and
graphics cards up a little past the TDP if you really, really try,
but even if you're running some distributed-computing application
that keeps your CPU at 99% utilisation all day long, you're probably
not exceeding the TDP. This is because different tasks light up
different areas of the processor, and also hit the cache memory
(which takes up a lot of real-estate on modern CPU) differently.
Tasks that all apparently cause the same level of CPU utilisation can
consume quite different amounts of power.
So taking TDP as a realistic maximum figure, a 108W-TDP graphics card
plus a 95W-TDP CPU give a peak draw of 203 watts just for the CPU and
graphics card. The whole system's realistic peak draw won't ever
exceed 300W, and probably not even 250W.
And remember that this is a ceiling power figure. Real-world power
consumption for this Core i5 system, even when you're playing a game
and working both CPU and graphics card pretty hard, could easily
average out at less than 200W, even after overclocking.
(There are also usually several differently-clocked CPUs in a given
lineup that all have the _same_ TDP. The slower models actually won't
ever draw that much at stock speed; system designers just like to
make sure a computer has enough cooling for the fastest CPU anybody's
likely to upgrade it to. This includes chips that haven't even been
released yet.)
There sure are 300-watt graphics cards out there, though, and you
don't even need to buy a dual-GPU card. As I write this, the
top-of-the-line single-GPU ATI graphics card is the Radeon HD 5970,
which has a TDP of 228 watts at stock speed. The top single-GPU
Nvidia card is the GeForce GTX 285, which tops out at 204 watts.
Overclock these with gusto and you could get very close to 300 watts.
There've been several graphics cards over the last few years that at
least push the 200-watt line. None of them have been mid-range cards
like the one you're considering, though, and I don't think any
mid-range card is ever likely to draw that much.
(Wikipedia have neat comparison pages for ATI and Nvidia GPUs, by the
way, which give TDP numbers with the other specs:
http://en.wikipedia.org/wiki/Comparison_of_AMD_graphics_processing_units
http://en.wikipedia.org/wiki/Comparison_of_Nvidia_graphics_processing_units
As you can see, the midrange cards have always had much less alarming
power draws than the top-enders.)
PSU efficiency, like a lot of environmentalist issues, makes a
difference to the planet but not much of a difference to the
individual user. Many PSUs these days have excellent efficiency at a
variety of load levels, but even if you've got a computer that draws
300 watts, 24 hours a day, then a 70%-efficient PSU will draw 429
watts from the wall, while a 90% efficient one (which will pass the
80 PLUS "gold" test) will draw 333W. Even if you pay a quite high
(for Australia) 20 cents per kilowatt-hour, the less efficient PSU
will only cost you about $42 per year.
One other tip: It's a good idea to have a spare PSU sitting on the
shelf, on account of power supplies' well-known tendency to die at
the start of a long weekend. Even if your standby PSU has a
considerably lower power rating than your in-use one, it should still
be able to run the operating system and 2D applications like e-mail
and your Web browser. This is a heck of a lot better than nothing
while you wait for a warranty replacement on a popped PSU.
--
Daniel Rutter
Atomic I/O letters organism
