Doubling the GPU computing power

Hello,

They are by no means the fastest cards, but for optimal results per KwH I recommend nVidia 650ti's. They will do 2 simultaneous units in approximately 3600 seconds if you have at least PCI-E 2.0 8x for each, and consume about 50w each (they are rated at 65w, but don't use that much doing BRP4). They only need one 6-pin connector each, and the two machines I have running with two cards each consume about 175w/hour and 220w/hour respectively (lower power unit's CPU is a 35w i3 3220t, and higher a 95w FX-6100). This means I can use inexpensive 400w power supplies.

The above won't raise your production much from 450's, but it will lower your power bill. If you also want to raise your output, a 660ti is still fairly efficient. It will cost you a little more than 2x as much as a 650ti, use 2x as much power, and give you almost (but not quite) 2x the results. They also need 2 6-pin connectors each, which means a larger and more expensive power supply.

I have found that, on the motherboard, you need at least 16x PCI-E 2.0 or 8x of PCI-E 3.0 to take full advantage of one low-end 600-series card (650 or 650ti); 8x on PCI-E 2.0 (or 16x on 1.0) equals about a 10% loss in output from bandwidth throttling.

I've had mostly similar results on the 650 / 650ti on CPUs from Core2Duo to SandyBridge i3 to AMD FX series. When you get into higher-end cards in this series, PCI-E bandwidth on the CPU itself also becomes important.

Absolutely. I have actual power meter readings for both 650 and 650Ti GPUs. They pull very close to 60W and 110W respectively.

Absolutely, but ...

... you really can't just make a blanket statement of 500W without pointing out that it all depends on the quality of components used, the efficiency of conversion from mains to DC and the honesty of the manufacturer in labeling the rated outputs, what the actual power draw from the wall will be, as well as (for recent systems) the availability of 12V power.

Modern systems require the bulk of their power to be 12V power. The only way for the average volunteer to get a handle on all this is to do a bit of research on hardware review sites. I've found this one to be useful in getting a very good feel for what to look for in a PSU. I've learned never to trust claimed outputs of unknown generic brands. For many branded units, it's always good to find out who actually made the unit in the first place. You can find out how to do this on the site I linked to.

Nearly 4 years ago, I bought a bulk lot of 300W PSUs. They were branded "Ipex" but were manufactured by Seasonic (a very reputable manufacturer) and there was a Seasonic model with identical specs that I found a review for. They were rated at 300W with 270W on the 12V rail. They have all been in 24/7 use in my systens, mainly in a sub-tropical non-air-conditioned environment and there has actually been one failure (out of 50 units) only. I've seen 500-600W units that wont last 12 months under these conditions.

So, for anybody thinking of upgrading your hardware, identify how much power you need, add at least 50% on top for safety and buy a quality unit that can actually deliver what the label says. To do that you need to come up with a list of candidates and research them on reputable review sites.

Yeah ya right... Sometimes I forget to go in to detail. Been building computers for so long I sometimes take for granted my exp. and others not having it. Sorry only human and I do forget things "the little things". Ok over all system wide specs always go over what you are planning to do. Like I built this desktop mainly for games such as the sims 3 but I added a bit more power just in case I want/need to do something else. The old saying "It's better to have and not need than to need and not have" :)

Agreed and well said. Always should use quality components.